TransGaming Technologies developer of Cedega (formerly known as WineX) has announced they will be adding support to Half-Life 2 in an upcoming version of the program version 4.2, scheduled for December 7th.
Cedega is a Windows-Linux wrapper that according to Transgaming allows Windows-based games to run on Linux, out-of-the-box transparently. Developer claims current version of Cedega supports popular titles such as: Max Payne 2, GTA Vice City, Battlefield 1942, WarCraft III, Diablo II, Half-Life, Star Wars Galaxies, EverQuest (full list here).