Rhythmbox with space for the upcoming Ubuntu One Music Store.
Updated MeMenu, with apparent support for IM and Social Networking. If you type in the box and press enter, it posts to your Facebook/Twitter/whatever Social Network(s) you set.
The full Social Network integration. I've only got Twitter set, but you can do Facebook, Flickr, and a bunch of other stuff too.
the other new theme, which is lighter.