Action Points (the APs in UA don't suffer from "extra life" syndrome)
Craft Points (drop the feats for crafting normal items though, that's rather absurd, after that you have a pretty wonderful system for a faster-paced game, especially if you tinker with other thing besides gold to fuel magic power)
Class variants (just allow them all and see what people do, they're all pretty rad)
Weapon Proficiency Groups (more weapon variety for characters w/ less feats without an upward power creep)
That was one campaign.
Current campaign is Gestalt (playing w/ less characters is easier to balance)
and Spell Points (easier for newer players.)
I pretty highly recommend everything in that book, I truly enjoyed it.
If you don't want the game to slow down, just use alternate classes, buying off LA, and maybe spell points if he wants to use it. The rest will slow the game down a little bit, especially the first time they're used. Weapon Proficiency groups is pretty easy, but not worth it for everyone. (Although it certainly was for me!)