D&D House Rules

Character Generation:

• For stats, roll 4d6, rerolling 1s, drop the lowest.  do that seven times, dropping the lowest stat. Make 3 sets of stats, use whichever you want.
• Reroll hit points at each level if the roll come up less that 25% of max (1's on d4/d6, 1's and 2's on d8 / d10, 1's, 2's, 3's on d12).

Healing:

• If you're NOT in combat and a healing spell/potion/scroll/etc. is used, reroll any dice that come up at 25% of max or less.  however, if the patient or healer is still in a combat area, then you do NOT get to reroll.  This makes combat casting a bit less precise, but reduces the risk that a valuable spell slot will come up short when healing is involved.

Arcane Magic:

• I think the two new spells per level rule puts an undue burden on wizards.  The cleric doesn't go through this bottleneck nor does the Sorcerer. Nor is the fighter forced to kill more and more creatures to advance--er, nevermind. In any event, to combat this spell shortage, Wizards get the two spells as stated in PHB, plus a number of spells equal to their Intelligence modifier.  This seems a fair increase without  unbalancing things from the core.
• Fast Learner Feat - Prerequisites: Ability to memorize and cast 2nd level arcane spells from a spell book. Effect: By taking this feat, the caster is able to learn more spells at each caster level. The caster learns 2 extra spells at each level. This is not retroactive and takes affect starting with the level in which the Feat is gained. Normal: Normally, Wizards gain 3 spells per level. Special: This feat may be taken multiple times. Each additional Fast Learner Feat taken adds 2 extra spells learned at each level from that point forward.

Movement:

• Drop the 1-inch grid maps. Instead, use a ruler. Most natural spaces and even most buildings resist following a perfect grid layout. Using a ruler also means not having to count squares and do strange pixelated spell effects and curves. This is borrowed from WarHammer rules, where natural lines are used with rulers.
• Also from Warhammer, a Ranged Attack aiming rule. Simply put, you declare a distance, then fire, then measure to see if you were right.  This doesn't apply to bows and crossbows, but does to ranged spells, particularly fireball type spells.  When a scaled map is used, the player guesses the distance/direction from the caster/shooter to fire the effect.  Then the GM or player measures that distance out along a line, and figures the effects of the spell based on that target location.  Optional Rule: If a character makes a Spot check at DC 15, then they know the correct distance plus or minus 20%.  If they get a DC 20 check, then they know the distance plus/minus 10%.  DC 25 gives them the correct distance to target.

We have more D&D 3 / 3.5 House Rules at the link.