I just scored a set of carbon bars off eBay for $40. They are one of the best upgrades I ever tried, and I regret waiting so long before trying them.

The ergo/aero shape of the bars in the locations where I typically like to put my hands is far more comfortable than the round aluminum bars I was using previously.

The ones I got are not a well-known brand (Carbotec, made in Taiwan), but they are similar in appearance to the FSA K-Wings.