Blip is sort of like a Twitter for music

It's a cool website where you can check out what other people are listening to and also quickly inform your friends as to what your currently playing.
The interface is really straightforward, allowing you to search for, play and share your favourite music tracks in real time. If you choose to register, you can set Blip to automatically update your Twitter, Friendfeed, Pownce, and other accounts with whatever songs you're playing.
It's an easy way to kill a few hours while you check out old songs you'd forgotten about and also discover cool new music. Here's the weblink for Blip.