I put a Sheldon Brown (R.I.P.) special 12-30 on my recently built TCR with a 50/36 compact crank. The percent change gets larger as you shift to through the larger cogs but remains close through the higher gears. I am happy with it so far. You can find the cassette here.
http://harriscyclery.net/itemdetails...gId=39&id=2369