PeerBlock

Overview
PeerBlock
The successor to the popular safety tool PeerGuardian, PeerBlock is a firewall with a difference. Unlike traditional firewalls, it protects your PC from intruders using a blacklist of sites in specific categories, including adware networks and known spyware providers.
PeerBlock is designed with filesharing in mind, and can also be set up to block websites with an anti-filesharing agenda.
You don’t need to worry about updating the lists manually – PeerBlock refreshes its blacklists regularly according to your preferences.