Stumble!
I just came across a fantastic plug-in for Firefox called StumbleUpon. I had heard about it awhile back on on digg, but I didn't get around to installing in until the past weekend. StumbleUpon allows you explore oodles of web sites based on the interests you designate. It's a great way to learn about new websites that you'd never happen across otherwise. You can also share your sites with friends and vice versa. I think of it as a more usable version of del.icio.us. Highly recommended.