Pidgin 2.6 adds audio/video support for Gtalk: "Pidgin, a popular, crossplatform, multi-protocol chat app, just got an important update to version 2.6. It's important because this is the first time Pidgin has supported audio or video chat over Google Talk. Even my favorite chat client for the Mac, Adium, doesn't yet support those features. Unfortunately, audio and video chats don't yet work in the Windows version of Pidgin, but they should be available soon.
The other very important update better (read: actually working) file transfers on Yahoo! and Google Talk. There's also some preliminary theme support, for those of you who enjoy building themes, but it's that feature is too new to have a selection of themes to choose from.
If you're not comfortable compiling an app, you can wait on Pidgin for a little while until the pre-compiled native apps show up. Speaking of native apps, Pidgin doesn't look bad on a Mac, per se, but it can't compete on looks against a Mac-like app like Adium.