The Linux Game Tome polled for the best Linux games and came up with a notable list of excellent games for Linux, free and otherwise. Frozen Bubble, a bubble shooter clone, took several categories, including Best Free Game. In addition to being a slick implementation with graphics, sound and music above and beyond what you normally get for free, Frozen Bubble also deserves mention for being written in Perl, using the SDL cross-platform multimedia library and SDL-Perl glue code.
Similarly impressive: PySol, a massive collection of solitaire card games implemented in Python.