I have a lot of IM accounts, mainly because my customers use different platforms and then I have my personal accounts as well. What I have been using for a long time was Trillan . It allows you to sing in to all of your accounts from one application. I also use Meebo, Meebo is a web based tool dose the same thing.
Things in Trillan have always seems to clunky for me and I could get my 100s o contact sorted the way I wanted. then I found Pidgin.
Pidgin is a FREE open source chat client that does the same thing as Trillan, but for me is a much cleaner interface and over all easier to use.
The only down fall I can see with Pidgin is that when I am brought in to a new group chat it doesn’t POP Up. Those dont happen to often.
I Have been a log time Trillan user, but things just were not smooth enought for me.