[Don Plumley]

Clearly the most important tool is parental involvement, etc. For younger kids, I think you are more concerned that when they search on "Bill Clinton" the first image that shows up isn't someone getting a BJ. I think this opens a great opportunity for dinner table discussion - if you walk into a public library you can find pictures/information about anything, it's just not as fast (or in high res close-up video!) as online.

Most good routers provide white list/black list and other control functions. By IP or MAC address you can set allowable times for access, disable IM, keyword blocking, etc. Newer netgear routers list these as parental controls for example. As a first line, I'd rather work at the router level than through filtering software.

I believe that a product called NetNanny is well-rated for the individual PC and has a very rich feature set (e.g. facebook monitoring, etc.)