Trillian is showing big players what an IM client is supposed to be, and it actually works while I - as well as others I talked to - couldn't even get Jabber clients to do anything (your mileage may vary).

I like how their stocks plugin let you change the web site you use to get detailed information (provided the site is REST-compliant, you need an URL that takes the stock ticker as an argument).

The RSS plugin is fun but obviously doesn't scale if you monitor dozens or hundreds of sources, and there's no obvious way to import a whole list of subscriptions (i guess in OCS format or something). You can float the plugin in a separate window, from the contact list.

The Winamp plugin doesn't work with Winamp 3.0 yet, but I'm not sure it was such a good idea to install the later. There's also a plugin to check POP3 email accounts (not IMAP4 as of yet) but it didn't work for me.

There's a total of 8 plugins overall, and I don't know how hard they're to do, so I wonder if Trillian is about to become a platform as successful as Winamp for third-party goodies.