you can change the preferences so you only receive messages from those in your contact list and exclude messages to multiple parties.
you can also turn it so that you cannot be added to anyone's contact list without your approval.
Those two steps alone go a long way in reducing the IM spam.
Gaim works with multiple services as does Trillian.
And by the way, you list aol's instant messenger in your profile. ICQ & Aim are owned by AOL -- and they intercommunicate, so, you already have ICQ.
