Net Nanny 7

Pros
Net Nanny lets you manage all of the installations from a web portal.

Cons
It does not work on Windows XP (but then you should have moved on from XP by now anyway).

The Verdict
: 9.95/10

Net Nanny is the most effective internet filter software.

Download - $28.99
Download + Backup CD -$33.99
Buy Net Nanny 7
How to Block a Website with NetNanny
NetNanny has efficient ways of restricting access to particular sites you don't want on your computer.