I use pidgin for my Instant messaging needs.
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it says about itself:
Pidgin is a graphical modular messaging client based on libpurple which is capable of connecting to AIM, MSN, Yahoo!, XMPP, ICQ, IRC, SILC, SIP/SIMPLE, Novell GroupWise, Lotus Sametime, Bonjour, Zephyr, MySpaceIM, Gadu-Gadu, and QQ all at once. It is written using GTK+.
I use it for AIM, MSN, Yahoo!, XMPP (gmail instant messaging), ICQ, IRC, Novell GroupWise, Lotus Sametime, and MySpaceIM
never heard of SILC, SIP/SIMPLE,Bonjour, Zephyr, Gadu-Gadu, and QQ