Keihen PWK's, Mikuni TM's, Lectrons
Those are your most common.
I am running the TM's because they are more common with the guys I ride with, so if i need parts I can get them while riding if I dont have them.
Any of the three will run great. Go with what you can afford and what parts are ezer to get. Just remember that the PWK's once drilled can not go back, where the other two can.