Block Offensive Sites:You can block most offensive sites using OpenDNS FamilyShield. It's free, and if your router supports it, it will work on your entire home network. If not, you can configure each device you want blocked.
Block Offensive Search Results:Enable and lock Google's SafeSearch. The other major search engines also have similar safety settings. (But be aware, these only block search results. They don't block the actual sites.)
Block Offensive Content in your browser:For Firefox there is a parental control addon called FoxFilter. It uses both a word filter (which actually works, unlike IE’s rating system) and a user-modifiable list of blocked and trusted sites.
Other:NOTE ABOUT SEARCH ENGINES: I've made the switch to DuckDuckGo.com. It's a well designed search engine, and they don't track you and filter you like Google does.