Adium is a fast and free instant messaging client which supports AIM, ICQ, Jabber, MSN, Yahoo!, Google Talk, Yahoo! Japan, Bonjour, Gadu-Gadu, Novell Groupwise, and Lotus Sametime. Adium supports beautiful WebKit message display, tabbed messaging, encrypted chat, file transfer, and more. Give it a try; you won't look back.
Adium is currently translated into Catalan, Czech, Danish, Dutch, English, French, German, Icelandic, Italian, Japanese, Norwegian, Russian, Simplified Chinese, Swedish, and Traditional Chinese.