If you are using Safari in MAC and are looking for an ad-blocker then you can try with GlimmerBlocker. There are many other ad-blockers but the problem with other ad-blockers for Safari is that they are implemented as awful hacks: as an InputManager and/or ApplicationEnhancer. WIth these types of programs you need to compromise the stability of Safari browser. These may often create problems with the new versions of Safari.
The good thing about GlimmerBlocker is that it is implemented as an http proxy, so the stability of Safari isn’t compromised. Moreover it is compatible with all other browsers. You can always upgrade either your Safari browser or GlimmerBlocker without any problems.