The newest version of Trillian
is great. It has all the added features I wanted before I switched over to it as my primary messenger. Trillian will incorporate all the major messaging services together, ICQ, AIM, MSN, Yahoo, and even ICR. It's great for people that do not want to waste a lot of resources on having 4 different messaging softwares open all the time. It's easy to install and easy to set up. It will make all your messaging work the same.
Try it out. :)