The best IM application that costs $$ is IM+ and it has a Today plugin. Worth the $ if you want to pay, but...
Palringo is free, and its good. No Today plugin, but it does run in the "tray" and stays active.
The major different between the 2, besides the cost: IM+ has Myspace IM support, Palringo does not. Other than that they both allow you to connect up to the major IM networks.
URLs:
IM+:
http://www.shapeservices.com/en/prod...tform=pocketpc
Palringo:
http://www.palringo.com/