The one I use is called AdBlocker, the dev is Yllier.
I had tested the load speeds when it first came out back before 4.3.1 and after it got a few updates most sites loaded slightly faster and some slightly slower but all ads were blocked.
I just tested it again now since you made me curious on how it actually handles sites with the new improved Safari nitro Javascript on 4.3.1.
Well unfortunately most sites do actually load slower with enabled but the ads are still blocked.
Thanks for making me check it again, before when I was on 4.0.1 it was actually worth having now I'm gonna disable it and recheck it if it ever gets updated.
Funny thing is I just recently recommended this app to someone in another thread and now I'm gonna have to change that.