In my seemingly never ending search for the ultimate Instant Messenger client, I recently discovered Digsby. I used Pidgin for a while (but stopped, thanks to the thick-skulled developers). I tried Trillian but decided I didn’t think it was worth, to me, what they charge for it (the free version doesn’t meet my needs), and MSN Live Messenger has frequently has problems communicating with Yahoo IM folks.
Digsby takes most of the features of a Trillian or a Pidgin but goes several steps further. Sure, they support all the major IM services (MSN, Yahoo, AOL, Google, etc.) but they also allow you to integrate your email, Facebook, Twitter, etc. right into the client so you can see when you get new messages or updates of what your friends are doing on facebook. Plus, Digsby has a very nice and highly customizable user interface. If you use IM, you should check out Digsby.