Cue David Brent!
While you can now contact me via all of the IM forms listed in the left-hand sidebar, I have got to recommend a Web-based solution that combines the best of all of them -- and allows you to communicate with everyone anywhere regardless of the app... while on the Web.
Meebo allows you to access all of your IM accounts -- AIM, Yahoo, GTalk, MSN, ICQ, etc. -- on the Web in one window.
It's pretty keen.
Most of my contacts are in AIM, but we'll see if this works in my favor!