The Free Internet Chess Server (FICS) is one of the oldest chess servers on the internet, and is a very pleasant place to play and socialise. Babaschess is without doubt the best interface to use on it, and sets a benchmark for high quality software regardless of cost. Of course, the nicest thing is, it's free!http://www.babaschess.net/
Traditionally, commands are entered as text in the text console, which is a very versatile and speedy way of doing things once you've learnt the language. Fortunately for those new to the server, you can access all the most useful commands and settings using the babaschess menus, by right-clicking, or through the info windows, such as the seek graph.
The interface is very highly configurable and windows, backgrounds, boards and pieces, move highlighting, sounds, console fonts etc etc etc can be tweaked and changed in countless combinations. There are also a few ready-made themes to try.
Babaschess supports UCI engines and its Analyze game, with its two score deltas for "?" and "??" annotations, is my favourite blundercheck from all chess software (although it would be nice if board sounds could be automatically turned off to stop it sounding like a machine-gun) !
Update Feb 2015: Perhaps the only shortcoming of the default package is the lack of attractive vector piece graphics. This problem has been solved by Gorgonian's Babaschess Downloads, an absolutely first-rate resource.
Visit http://www.freechess.org/ for more information about the Free Internet Chess Server and to register for an online username/handle!