Tool box of web 2.0 tools

I never knew this existed. I had already explored the Library thing and made a book shelf, so I explored something different. I stumbled upon;) StumbleUpon. This website is cool. After registering, you pick topics that you are interested in and the website shows you a page. You click on thumbs up for "I like it" or thumbs down. It starts to remember your tags and it gets smarter by bringing up website that you like.