Adium X

For anyone wanting to do instant messaging on Mac OS X I can thoroughly recommend Adium X. It’s a multi-protocol client, which means you can chat with people on MSN and ICQ and AIM and iChat all at once. It’s clean, stable, and has an amazingly cute icon (which you can change btw). I dabbled using Fire for a while and I also used the Microsoft MSN client for a bit, but Adium is definitely more stable and better to use IMO.