-I use a 30 second timer, personally, during combat. If your character has to decide and act out their entire round within 6 seconds, requiring the player to at least decide on the actions within 30 isn't a bad idea, after all.
-When purchasing items, I have the players either come up with a list of stuff they want in between sessions, or before hand that they can pull from when they have the wealth for it. That way, all I have to do is run down the list and approve/disapprove items when it comes up.
-If the player doesn't know how their spell works, it fizzles. This fixes the "Wait 5 minutes while I track down and look up how this spell I've known I was going to use for three weeks works" issues.
-Rules discussions limited to 1 minute. If you cannot find the reference you are disputing within that time, we'll go with my way and look it up and discuss changes/adjustments before the next session, in order to prevent stalling out the game.
-No summoning in combat. It's just a gentleman's rule I try to keep with the players in order to keep one player from having 17 different sets of actions in a combat at the higher levels.
-Have page and book references listed next to your stuff. Then again, I ask this in smaller games too, in case a question on something comes up.
And +1 to everything Dither said.