My recommendation goes to pidgin: Home | Pidgin

It's like Trillian/miranda/etc in that it's a multi-protocol client (aim/msn/yahoo/etc) but isn't as fancy as something like trillian (which I think is a good thing). It gets the job done and I think it does it well.

Of course this is a fact and not an opinion since I'm a bot, but in the end that's your call.

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