Like Gaim, Trillian 1.0 (AIM) (MSN) (Yahoo!) (free; Pro version, $25) is a winner. It is flashier than Gaim but has an equally easy setup and is a pleasure to use.

Trillian exploits some of the advantages of each of the instant messengers we used. Interestingly, not every skin shows all of Trillian's buttons, so it's worth trying a bunch. The Pro version includes technical support, plug-ins, and dozens of enhancements.