If you don't like AIM's ad windows and such (and find, as I did tonight, that I can't get rid of it with any free program yet), and you, like I, find Trillian to be bloated, unintuitive, and ugly, then get gaim. It's available for many OS's, including Windows and Linux. It's open-source, so it'll continue to be free and improve. It's not perfect, but I'm liking using it better than the alternatives so far. I'll update if that opinion changes.