For posting: - invitations to games (you can also use the New Game menu or go straight to the Chess Invitation) - information about upcoming tournaments - discussion of games (please limit this to completed games or discussion on how a game has arrived at a certain position ... speculation on who has an advantage or the benefits of potential moves is not permitted) - links to interesting related sites (non-promotional)
Also, check out Chessville and do a search for interfaces. You can get free ones to use on FICS.
I like Winboard which also serves as a chess engine and PGN reader.
Jin is a java interface and very good. Also Thief and Interchess are available free. If you cannot find the specific program I mention,
let me know and I'll find the URL and pass that along.