I used to use AIMM, which was a very clean and simple AIM client for PPC 7.6-9.2, but it relies on TOC (which AOL has discontinued). The AOL client is disgusting and I imagine anything from Microsoft or Yahoo would be the same, so currently I'm not aware of any decent working clients. Of course, by now almost everyone in my social circles has stopped using AIM in favor of Facebook chat, which I think runs on Jabber, so maybe I'll give JabberNaut a try.