Please include
3) Psi, "Instant messaging as free and open as it should be."
"Psi is a free instant messaging application designed for the Jabber IM network (including Google Talk). Fast and lightweight, Psi is fully open-source and compatible with Windows, Linux, and Mac OS X."
Psi also supports encryption with gnupg/openpgp keys.
(Pigdin might be ok for people who just use icq or msn... but it doesn't support Jabber properly)