StumbleUpon is an extension that lets you 'channel surf' various websites recommended by other users of the extension. It brings you to sites based on other people's recommendations and your own reviews of other sites you have visited (you can give them a quick 'thumbs up' or 'thumbs down' and it tracks all of this).
It goes further in depth, including user blogs, etc, but without getting into all of that, it is just cool to flip through random sites when you are bored.