The best guide book for Costa Rica is the "Costa Rica Handbook" written by Christopher P.Baker published by Moon Travel Handbooks. It's very recommended and detailed ! If you are planning to go there between December and April that is exactly the high season over there.

Now let's see: we would recommend to try and avoid doing the same roads more than once since they are very shitty roads, full of potholes and many times one lane. If you rent a car make sure it's 4 wheel drive. It's very helpful there. Don't be fooled by the term Trans-American Highway, it's not so impressive in reality... I can't think of a real reason why you're better off starting from one side or the other. You may want to leave the rougher side for the end.

You might want to spend some time in the San Jose area and go from there to various locations (don't stay in San Jose itself - it is the ugliest city on earth - ok, maybe I got a little carried away but don't expect anything from it, you really don't have to see it if it doesn't fit in your plans). I don't know if you are into budget traveling or a little more expensive, maybe you could get some good deal at the Marriot (on account of being Intel employees-it's right across from the site so you could hop over there to read cc mail, I think this is something you Intel folks do on vacation, right ??) It's a very fancy hotel but the Cariari area is a nice one... That's where we lived and it's right next to San Jose. From the San Jose area you could take a few day trips like:

• Orosi valley (very nice valley) and Cartago (used to be CR's capital in the past, some ruins and a church to check out). Cartago is small and you really don't need more than 1-2 hours there to see the worthwhile stuff there.

• Volcan Irazu is about 2 hours from San Jose, it's right above Cartago (make sure you go there very early before the clouds settle and you don't see a thing but not before the park opens...also, expect to pay $6 each at every volcano/park). Oh, and the 'get there early rule' applies to all the volcanoes.
  

• Carrara park is 1.5 hours from San Jose, it's very nice ( you can also combine it with a trip to the west coast but give it a full day), you should see there some wildlife and the almost extinct Scarlet Macaws. At 8 am and 16 you have a chance to see them flying in and out to the park (the guide will have more details on this). It is recommended to hire a guide there, you'll see much more wildlife that way and they have interesting stuff to tell. Freddie is recommended there.If you can stop at the Tarcoles bridge just east of the park, you can see alligators and marine birds right from the road. Keep your eyes open and your ears wide open. The Scarlet Macaws have a very distinct loud and sharp shout. So if you hear something like that look up, they usually travel in couples and from earth they have a cross shaped silhouette. Oh yeah, take binoculars with you !!

• Volcan Poas is highly recommended. Less than an hour from San Jose and a beautiful site to see. The drive up there from the Pan American road is also very nice, with many cofee plantations on the rolling hills. At the top you can see the smoking (yes! actually visibly active!) crater.

• Zarcero is nice with it's man sculptured garden but that is all there is to it. The area around it is nice to ride around. So if you can combine it with other places great but don't go out of your way too much to see it.

• Sarchi is a tourist trap full of tourist junk. Then again if you are into furniture maybe you'll want to see it because it's supposed to be the center of the furniture and the non-existent arts & crafts in CR. Once again, the area is nice to drive around.

Manuel Antonio is a nice and organized park, you are almost sure to see the white faced monkeys over there, Iguanas, rodents and if you are very lucky a sloth ! You are also sure to see many travelers over there... but it also has a beautiful coast and it's definitely worth a visit.
The accommodations there on the beach are between very cheap and very expensive. You can find a place very close to the park. small tip in the park - don't use the services of the guy that wants to take you across the creek with his boat for 2 bucks a person each way, it's about a half a meter deep right next to where he passes. Once again, if you are into expensive lodging "El Parador" is very nice, the rooms are fine and the food is ok. Doron went there once with his friend Noa and they stayed at a much cheaper place called "Hotel Del Mar" which he said was sufficient.
BTW - on the way to Manuel Antonio after Carrara park and just before the coastal village of Jaco there is a magnificent hotel called "Villa Caletas". It's very recommended to stop there even just to walk around and see the place. It was designed by a French dude and it has a spectacular view, an amphitheater where they have live music sometimes, a panoramic pool and sculptures all around. Check it out ! Oh, and in the season the park should be a good place to scuba dive.

Guanacaste is an area at the north-west of CR. It has a more hot and dry savanna like climate and it has nice beaches, full of tourists. Nicoya Peninsula is part of it and that's where most of the beaches are. You might want to take a ferry to the peninsula from Puntarenas, it might save a few hours of driving. A Place we didn't see there but would have, had we had more time was Rincon de la Vieja park (just north of the city Liberia). The beaches that were recommended to us were Flamingo and Tamarindo - that's where the gringos go... We went to Playa Hermosa which was a quieter, more private beach up north. About surfing, we can't comment, the guide will say.

Arenal is the most active volcano with lava pouring out of it and a huge lake right beneath it. We think that the lake is very popular among wind surfers. We never got to see the shpritsing top of the volcano, but we heard it rumble. If you're traveling there in the dry season you have much better chances to see it. We stayed at the Arenal Observatory Lodge which is right at the foot of the volcano and has a great view if you order in advance. The service / management though sucks !!! there are cheaper places before you get so close to the volcano. There are also the "Tabacon" hot springs right by, if you are into that muddy experience...
BTW- we ate there a nice smoked meat meal at a place called "Xiloe" (and I think we didn't mention yet that you should lower your culinary expectations quite a bit before going to CR...) When we were there we did the mistake of driving from the volcano counter clockwise around the lake, it took us forever because the road there was at a very poor condition, it's probably worth doing some extra mileage on a better road. Go to the lake through Canas (pronounced Canias, but we don't have the ~ to put on the n) and Tilaran then back the same way. The volcano can be reached from the South through San Ramon.

Monte Verde is a private cloud forest owned by North American Quakers who are doing a good job at preserving it. One of their methods to limit the amount of people going to the forest is maintaining the non-maintenance of the road leading to it from the Pan American highway. It's about 30 kilometers long and it takes about 2 hours, horrible, horrible road !! They also limit the amount of visitors to the park to 100 a day or at a given time. Still, the reserve is very lush and beautiful. Hugh trees and waterfalls. Many humming birds and if you are lucky wildlife, we didn't get to see too much of it there (though we did see birds, insects and peccaries) but we were very glad we went and if it hadn't been for the terrible road, we probably would have gone back there when my parents visited us.
You might want to visit the near by reserves as well, see what the guide says about them.

The Caribbean / Atlantic coast is a different experience. The ride there from San Jose to Limon is about 4 hours and right after you go out of San Jose, between San Jose and Guapiles, you drive through a very nice cloud forest reserve (can't recall the name) so you probably want to drive there at daytime (it's also the place with the most traffic accidents in CR so be careful).
We were at the same village twice, it's called Punta Uva and it's almost the most southern part of CR before the border with Panama.
Puerto Viejo is also nice, kind of Sinai style, laid back, restaurants on the beach, dreadlocks, lots of drugs there too and crime too.. Punta Uva is smaller and quieter and has a nice beach too. There is a nice simple Italian restaurant there and we had great Caribbean style fresh fish at Selvin's (the man there asked us to wait while he went to bring our fish from the fishermen...). In Puerto Viejo there is a highly recommended restaurant called "El Jardin" - we had great typical food there.
In Punta Uva we stayed at two places: first time at "Miraflores" B&B - a nice atmospheric place run by a North American woman called Pamela (you can give her regards from the couple of guys from Israel who tried to fix her fax...) - we saw a sloth in her backyard !! The place wasn't the cleanest but it's located right in the jungle which is cool (well not cool but COOLLL) You can shower half outdoors while looking into the jungle and listening to the jungle animals.
The second place we stayed at the second time was cleaner and run by a very nice couple (at least when we were there), it's called "La Isla Inn". Personally, we preferred it.
OK, as far as places to visit there

• Manzanillo is the jungle closest to what we expected a jungle to look/ feel like. Mud (well, it was the rainy season but then again remember that at this coast there are 300 days of rain a year...), sweat, leaches, thick vegetation, lots of wildlife (howler monkeys, white faces monkeys, toucans & other birds, sloths etc.) and secluded beautiful white sand beaches with plenty of coconut trees along (watch your heads!). When we went there the second time we worked hard on cracking a freshly fallen coconut by ourselves and it was definitely the best both of us had ever had, delicious!!!!!!!!! Take a lot of water with you when you go there. Even though we did, Irwin (my brother's partner) dehydrated and was a little sick... If you see there a couple of friendly dogs that will try to escort you give them our love (we called them Max and Tova) and they followed us around all the way (actually we followed them) but then again we might have seen less wildlife because of their presence.... Once again, we are not into diving but we heard that Punta Uva is a good place to dive.
• We also visited the Cahuita park which was ok but we hardly saw any wildlife there. We were told that there is a nice coral reef there, good for diving.

Tortuguero is also on this coast only norther and can be approached only by plane or boat. We weren't there but it's supposed to be similar to the Amazon, one Israeli was eaten there by the crocodiles when he took a swim and the place is famous for its tortoises but you need to check if it's the right season to see them.
BTW - skip Limon, there is nothing to see there and it's not too pleasant/ safe either.

The Corcovado park (Peninsula de Osa) was highly recommended to us but we never made it. It is supposed to be the least developed park and so the most unspoiled one, full of wildlife. If you go there you'll need a few days (4-5), I'm pretty sure you can't go there by car. This is the rougher part, access to there and in there is very difficult but everybody that went there said it's amazing and well worth the effort. Get a good map of Costa Rica and if a road doesn't seem like a main one on the map, prepare yourself to the worst dirt road in reality.

• Scuba Diving in Costa Rica.
• Map of Costa Rica.
• Country info.
• About the Costa Rica Handbook we recommended.
• Cool site about CR.