Trillian is a multi-network chat client that currently supports IRC, AIM, ICQ, MSN, and Yahoo! Messenger. It supports all of the features you've come to expect from a good IM client, including but not limited to docking, multi-line edit boxes, buddy alerts, multiple connections to the same medium, a powerful skinning language, easy importing of your existing contacts, skinnable emoticons, logging, global away/invisible features, and a unified contact list. Trillian is completely free with no nag screens or built-in ads.

Limitations:
This program by default will try to install
* The Weather Channel Desktop
* Ask Toolbar

You have to make sure you uncheck the install of the Weather Channel Desktop

Also for Ask Toolbar you have to uncheck to items
1. Enable address bar search feature
2. I accept the license agreement and want to install the free Ask Toolbar