Psion
Adventurer
In Trailblazer, iterative attacks work kind of like a monk's flurry of blows -- at BAB +6, you can make two attacks in a full attack, each at a -2 to attack (so your attacks are -2/-2 rather than 0/-5). Then, every +5 BAB past that, the penalty is reduced by one.
So at BAB +16, rather than getting attacks at +16/+11/+6/+1, you get +16/+16. Both your attacks have a good chance of hitting, rather than having one at good, one at so-so, one at hmm, and one at "20 always hits, right?".
Yeah, that.
Supposedly (didn't run the numbers myself), you actually get a damage boost except in corner cases.
After reading more of Trailblazer again, I'm thinking of using their take on action points as well.