You can find all sorts of Safari add-ons at Pimp My Safari.

There is also Saft, which is much more than an ad blocker (it's good to encourage Hao Li, a terrific hard working developer who usually updates Saft within 24 hours or less of a Safari update). And a simple ad blocker is SafariBlock. There are others out there.

I hope this helps.


Edited to add :

DOH! Soulwar beat me to it.