Chess Links

Places to Play Chess Online

Freechess.org - a great free Internet chess Server - lots of variants and tournaments.
chess.com - Good place for playing longer correspondence games.
Internet Chess Club - Good place to play - price is fairly high.
Gameknot.com - Pretty nice correspondence type games. Seems limited compared to chess.com
Chessboss - Chessboss has very few players and it is very hard to find a game. It runs completely within the browser. I find the limited number of opponents makes it not worthwhile.

Jin Chess Client - Good client to connect to FICS or ICC runs on Linux, OS X and Windows - works the same everywhere.
Fixation - newer program - OS X only - currently being developed.
Visir - An alright client - runs on OS X, Linux and Windows - interface is a little hard to use.
Eboard - pretty good client - Runs on Linux - nice interface
iNemesis Internet Chess - I have not had a chance to run this one yet.
Babaschess - This is the best interface for Windows users. It is very nice, works great for all of the variants. Too bad it does not work everywhere.
Ichess Pack - Good interface for the iphone. Has some good training options.

Chess Position Trainer - Great tool for learning openings and having a place to go back and review what you learned.

Chessgames - Provides a good community to learn and study games of strong players. Opening Explorer is interesting as well - although it is not 100% usable without a subscription.

chessup.net is a great tool for creating chess diagrams.
DiagTransfer is a free Windows program for creating chess diagrams. It has some advanced features and works with Crosssover Office. It might also work in Wine.
pgn4web is a good way to share entire games online.

These often have a lot of functionality that is more than just a chess database.

SCID is an open source database that will meet the needs of most casual chess players for DB functionality.