IChat

iChat is the built in instant messaging client for Apple's own network as well as other networks. It supports the iSight camera.

The current version is 4.05 and has support for 5 account types:
 * MobileMe accounts
 * Mac.com accounts
 * AIM accounts
 * Jabber accounts
 * Google Talk accounts

There is also support for local area network chatting using Bonjour.