aggregates twitter, pownce and facebook with a lot more rss feeds to social networking sites coming. See the Vote page for what they're working on. Contact me for a beta invite
Iminta has a cool thing going for it: you can put your followers in groups and specify which group sees what... I really like the idea of variable resolution for social feeds. Still in beta as of 3/16/08
Socialthing! is in private beta - see everything that's going on with your friends in all the sites you use, easily figure out where you're missing connections with your friends, interact with multiple sites at once, and more!