I have been using OpenDNS for some time now and I must say it is excellent. They say:
“We make your Internet safer, faster, smarter and more reliable. It’s free, and there’s nothing to download.”
One of the major benefits of using OpenDNS to handle your DNS lookups is that adult sites are blocked. You can set the granularity of the filter if you register with them but by default, if you use their DNS servers, you get filtering by default.
as your nameservers (preferably on your router) or on your PC.
Check out OpenDNS http://www.opendns.org for more details.