Recently out of private beta, multi-protocol super client Digsby pretty much does it all for me: It's combined four separate desktop or web applications into one - so far it's definitely a keeper.

As an Instant Messenger application, Digsby allows conversation between AIM, MSN, Yahoo, ICQ, Google Talk, and Jabber logins. For email it accepts Hotmail, Gmail, Yahoo Mail, AOL/AIM Mail, IMAP, and POP accounts, It also a pretty nifty two-way social networking client, and collaborates with Facebook, Twitter and MySpace. More are promised soon. I would like to see a bit more responsiveness in the Twitter client but if you let twitter@twitter.com run in chat it's pretty much instantaneous. Check out all the features here.

They seem to have a good support system, installation was a breeze. The interface is highly customizable with skins and allows a great many user preferences for notifications and other options. Nice touch that I only have to set those once, and even when installed on another computer they remain the same.

Maybe someday they'll incorporate aggregating feeds into the equation, but even so...I like it!