Nimbuzz Messenger is a free chat app & lets you make cheap international calls!
Skype, RenRen, Facebook Chat, MSN, Yahoo, ICQ, Google Talk, VKontakte and more. One app, all your messaging.
eBuddy is a free web based messenger that enables you to chat with your MSN, Yahoo, Google Talk, MySpace, Facebook, ICQ and AIM buddies. No downloads required!
Slick messenger (ICQ, Yahoo, AIM, MSN, Google Talk, Jabber, Facebook chat)