I was very impressed when I saw the first demo of WebOS quite a while back. I loved the way they integrated SMS, email, and social media all into one stream. Their point was that the most useful view was one oriented around the people, not the media. I think that's a very good point.
I've heard that FriendStream on HTC is pretty good but I have a samsung device.
I'm a big fan of Tweetdeck which brings together four (currently) social networks. You can post to all four at the same time, for those soap box moments :-)
I'd like to see an app that brings together EVERYTHING! even the voicemail and call log!
Am I asking the impossible?