I only have a few I can think of off-hand:
Spell Focus gives +2, there is no Greater Spell Focus.
Power attack is half benefit for off-hand weapons, and half-again benefit for two-handed weapons (and one-handed weapons wielded in two hands) - this basically makes it an increase to the Strength bonus.
Um... those are pretty much the only things I can think of off-hand. I might let Improved Crit and Keen stack as well.
I have a bunch of other house rules as well, but these are the only ones that are sort-of 3.0 throwbacks.