pidgin, Trillain, and Miranda all connect to the same clients. Trillian i know also connects to GTalk and Jabber clients. I dont think Pidgin or Miranda does that.
There is nothing that includes XFire. That is written specifically to be used for gaming. It was written to allow for messages and server stats. Which no other IM client does. So you will never find a IM client that incorporates XFire.