There's squidGuard which I use and there's also Dan's Guardian, which seems has more features and is more configurable, but I have not tryed it out. squidGuard can be downloaded from techgeeks.com I _think_ not too sure though

but Dan's guardian is available from dugog.net.
If you have any questions about squidGuard drop us a line and I can try to help you out

Cyrus Bharda