Raptor 0.97a
The latest new interface to use on FICS benefits from cross-platform support, a colourful console, easy window management, and UCI engine support for analysis. It's clean and mean and heading in the right direction!
http://code.google.com/p/raptor-chess-interface/Chess Assistant Club
A commercial quality interface for playing chess on the internet. Apart from the normal playing mode, there are rooms for tournaments (which are particularly good fun!), teams and correspondence chess, an online database of your played games, and funky features such as autocommenting using UCI engines. You can also connect using a flash interface.
http://chessok.com/?page_id=145Babaschess 4.0
It's lucky playing chess on the internet is such a productive way of spending my time, as I seem to spend a heck of a lot of it using this piece of software! ;-)
Read more in Pick of the Best...BabaschessJin
A good alternative way to access the Free Internet Chess Server is using Jin. It is functionally much simpler than babaschess, but has some attractive and interesting piece sets, and a good solid feel. I find it particularly good for my netbook's 1024x600 screen. Here are a few more piece sets. A slightly more reduced version is the Jin java applet, which you can use directly in your web browser.
http://www.jinchess.com/Playchess
Covering most of the top grandmaster tournaments live, the playchess server is one of the best places to watch live chess for free. You can use a nickname for free for 30 days, after which you need to enter as a guest (or create a new nickname!). This software is also included as a part of ChessBase Light 2009.
http://www.playchess.com/Ectool 7.01
If you play correspondence chess by email (such as on IECG), then this former commercial program, now freeware, is a popular choice for managing the games. As well as time-keeping, it can connect to your POP3 email account to send and retrieve moves.
http://rebel13.nl/windows/ectool.html