Here are some links to get you started with open source chess programs and software.

For a commercial/paid chess analysis client, I strongly recommend Chess Aquarium. I use it for managing my database and analyzing my past games. You can install any UCI compatible chess engine to it. You can purchase Aquarium from ChessOK. Don't get the fancy version with deep rybka, since now there are open source engines out there that are much stronger than Rybka there really is no point. In my opinion Aquarium is MUCH better than the Fritz client. However, you don't need to spend a dime to have excellent chess software. See below.

Chess.Com itself has an extensive downloads database:

http://www.chess.com/downloads

Discussion Forums:

http://www.open-chess.org/index.php

http://www.autochess.com/forum/

http://rybkaforum.net/cgi-bin/rybkaforum/forum_show.pl#bid9

Engines:

Some awesome open source engines include:

Houdini 1.5 (formerly the top engine, now there is Houdine 2.0 but that one is paid - I bought it but frankly 1.5 is awesome enough). Houdini is a tactical monster.

Komodo 3...this is a great engine that is more "human like" in its moves. It is expected to become the #1 engine soon when they release a multiprocessor version. Consensus is it does better in positional play.