From what I've seen, Spycraft seems to do this the best. You get a certain number of action dice each mission which you can use in a wide variety of ways (including healing yourself, adding to Defense/AC, and confirming criticals). What really makes it cool, IMO, is the the GM get's action dice too. Each time the GM awards one to the PCs, he gets one too. The GM doesn't have to use them but they are there to help when the dice don't go your way. In fact, Spycraft encourages the GM to hand out action dice to your players, so he gets more too!
In my D&D campaign we used a mix of action dice and action points. You could spend them to reroll a die or even use a feat you didn't have for one round (but only if it was "cool"). We even used them for interesting, out of combat effects. Once, the druid wanted to cast treeshape on some elf PCs so they could hide when their cart was inspected by drow guards. Its a personal range spell, but I let him blow two action dice to cast it on the two other PCs. This is a way to make the rules step aside when they get in the way of a fun game.