FICS would serve the purpose, I'm not a huge fan of the FICS server but it would work. The only drawback being the interface is a bit cryptic to new users.
I'd much prefer using the Chessbase / Playchess.com server. 'course that has a drawback in being only available to windows users as there are no *nix clients available for that server (but it's oh so nice).
I really see no problems with using Yahoo. It provides everything we'd need.