Pidgin is a free all-in-one IM software that has support for many different protocols.
I mainly use MSN and Skype, but also occasionally get contacted on GTalk. Pidgin can support all three of these, which makes life a lot simpler. Instead of managing three different applications, i can use one. Not to mention its support for both windows and linux. I can now access my MSN on my linux rig!
The tabbed conversations window is quite good, saving on precious windowspace.
Have a look at it..