The stock Android browser is nice and has always gotten the job done for me, but I recently tried two browsers which are competing for default status on my phone:
Dolphin Mini
Miren Browser
Both browsers are attractive, relatively lightweight, and add features without sacrificing simplicity. I strongly encourage anyone to try them out and decide which one is best for you.
If you're looking for a more full-featured browser - including extensions - then you should check out
Dolphin HD if you haven't already. It's a little clunky in my opinion, and the Dolphin Mini UI is more attractive to me, but it's definitely the most feature-full browser I've tried.
Opera and Firefox are both promising, but neither is ready for prime time on Android for a variety of reasons. Skyfire might be good if you're looking for a social browser with Facebook integration, otherwise there's no reason to use it over the others mentioned above.