Jin is a Java client for various chess servers. It currently supports the Internet Chess Club (chessclub.com) and the Free Internet Chess Server (freechess.org) but is designed to be able to support any chess server.
Best and simple fics/icc client, removes everything but the chess. (which is most important)
Best linux client for ICC. Only drawback is that it crashes occasionally. The other Java client crashes more often so this is the best there is.