Jeff Rient's Big Purple D30 Rule
Once per session each player may opt to roll the Labyrinth Lord’s big purple d30 in lieu of whatever die or dice the situation normally calls for. The choice to roll the big purple D30 must be made before any roll. The d30 cannot be roll for generating character statistics or hit points.
Of course, my d30 isn't purple, but you get the idea.
Critical Hits & Fumbles: I intend to include these. Some people think it ends up screwing over the PCs, but as long as crits and fumbles affect monsters too, I say it's fair. The exact charts are in flux, but criticals will most likely include extra damage, gaining a free attack, and knocking an opponent off his feet. Sample fumbles are things like dropping a weapon, breaking a weapon, or losing your next turn. "Nat 20s" = crits and "Nat 1s" = fumbles. Using the d30 to hit means any roll of 20+ is a critical.
Quaffing: Taking a stiff drink (ale, wine, spirits) can restore temporary hit points, but runs the risk of getting drunk and gaining temporary penalties to attack rolls.
Follow Through: Killing an opponent in melee allows a free "swing through" (cleave) to an adjacent foe. Magic-users, thieves, and clerics lack this ability.
Trained warrior: Fighters (and only fighters) get one attack per level vs. creatures of 1HD or less if they (the fighters) do not move that round.
This list is far from final, but it should give an idea of the direction I'm going with combat.