• Dungeon Master's Guide Variant Rules:
  Ability scores (p. 19): To generate characters, use a 30-point buy system.
  Variant, Power Components (p. 96): Admissible (Using rare/expensive components to substitute for XP expenditure when casting spells) .
  Variant, Automatic Hits and Misses (p. 64): A 'natural 1' counts as -10, and a 'natural 20' counts as a 30.
  Variant, Upkeep (p. 142): Admissible (characters must pay a certain amount to maintain themselves each month; must be in line with their social status or lose honor).
  Variant, Story Awards (p. 168): Admissible when appropriate.

• Song and Silence Variant Rules:
  Variant, Tougher Tumble Checks (p. 37): Imposes penalties for terrain type and darkness.
  Variant, Tougher Tumble Checks (p. 37): To tumble and escape an attack of opportunity, a character must make an Tumble check opposed by a d20 modified by the enemy's Reflex save.

• Psionics Handbook Variant Rules:
  Variant, Psionics are Different (p. 39): Psionics usually don't affect magic, and magic usually doesn't affect psionics.  When they do conflict (e.g., psycholuminescence manifested inside a darkness spell, the power or spell with the higher level dominates; otherwise the power or spell cast more recently dominates).

• If Thoughts Could Kill Variant Rules:
  Variant, Power Scaling Rule (p. 36 of the pdf): Pay additional power points to augment damage.
  Variant, Secondary Disciplines and Variant Powers Discovered (p. 37 of the pdf): Psions can choose two subdisciplines which are manifested as if with their primary discipline ability score.  They also use the chart to find how many power points and powers they gain per level.
  Variant, Spells as Powers (p. 40 of the pdf): Not admissible.

• Any and all feats from WotC sources are allowed.  Feats from 3rd-party sources are also allowed pending the DM's decision.  Regional feats from the Forgotten Realm's Campaign Sourcebook, become "open-ended" ancestral feats, meaning the player must invent a story about their character's ancestors to gain the feat. 
  

• Crossbows can be fired at an adjacent target without drawing an attack of opportunity from the target.  Other creatures threatening the crossbow-wielder are allowed attacks of opportunity against her however, for firing a missile weapon.  Loading a crossbow draws an attack of opportunity as usual.

• A loaded crossbow be used to flank an adjacent target.  Weapons with reach can be used to flank opponents within the area they threaten.  Thus, a character wielding a ransuer could flank an enemy if he is directly opposite another teammate - he does not however have to be adjacent to the enemy, since his weapon has reach.  This rule is probably implied by the PHB, but it has been added here for clarification.

• Iaijustu damage in normal combat applies to the first strike against a flat-footed opponent when the weapon is being drawn.  It cannot be applied to unarmed attacks.  Perhaps this could be better explained in the OA book so it wouldn't need a house rule.

• To fire more than one arrow or throw more than two hand-held missile (assuming one is held in the off-hand ready for use), a character must also possess the Quick Draw feat.  In other words, to attack multiple times in a round with a bow, a character must have the Quick Draw feat.

• Creatures immune to certain weapons are not threatened by them (e.g., a nonmagical sword vs. an incorporeal creature).  If a creature is not threatened by a weapon, it cannot be flanked by its wielder.  Wielders of "ineffective" weapons are allowed attacks of opportunity against opponents they cannot hit (though it does them little good).

• Wielders of weapons that cannot affect a certain creature cannot use the aid another action in melee (PHB, p. 135).

• Experience for "skill-based" adventures equals (character's skill rank) x (number of successful uses) x 10, summed for all skills used.  This is a system I made for those adventures where most of the action revolves around role-play and a lot of skill checks, such as a ninja spying on the local temple.  To be counted for experience, a the use of a skill has to be important (e.g., not hiding while there's no one to see you).
  
  For example, a ninja's mission requires her to spy on the local branch of Temple Makura.  During the adventure, she uses the following skills in important situations, with the following experience award (in this case, the ninja is a 4th-level character, and the first three skills are maxed out):
  

  Skill Successfully Used	Ranks	Number of Uses	XP
  Hide	7	4	7 x 4 x 10 = 280
  Move Silently	7	4	7 x 4 x 10 = 280
  Bluff	7	1	7 x 1 x 10 = 70
  Use Rope	2	1	2 x 1 x 10 = 20
  Open Lock	6	2	6 x 2 x 10 = 120
  TOTAL XP			770 XP

• Role-playing awards for minor instances equal 10 x character level, and five to ten times that for major instances.  This is equivalent to 1% of the XP required for the next character level for a minor award, and 5~10% for a major award. 

The Wu Jen