Here are a couple of fun things I found recently that I thought were interesting:
Gist - Most people have probably heard of github, but Gist seems to be a new service they are offering that will let you post code snipits, kind of like pastebin. But with Gist, you can share, make changes, fork, add files, etc. via git! To actually modify what you put there via git, you'll have to have a free account, but sharing code and pasting via the web interface requires nothing at all.
Ohloh - I have to admit, that I just don't get social networking yet. I can't seem to bring myself to really get into all the facebook and myspace and all that. I'm probably just getting old. This is one site that actually makes me think there is hope for the concept though, as it actually provides interesting metrics and information about open source projects. It found contributions I had made from years ago, and let me tie them to my account.