Unquestionably it requires a lot of focus to keep up and learn, but British freelancer Robin Brown has smartly assembled a list of 30 such tools and some primers on using them.
The usual suspects are there: Twitter, Flickr, Digg Delic.io.us and the like. But there are also some good off-to-the-side tools for mashups and other work. It's a good resource that serves a core curriculum for the student of new media.