Tux Racer!
Credit:Wikipedia
Starring Linux mascot Tux! Tux Racer, originally released in October of 2000, was named one of the best in 2007 under the category of free software by PC Magazine. The game features Tux sliding down a mountain slope with the objective of catching all the fish. Don't be fooled if you haven't played, this game's harder than it looks.
The game gives you a number of options, letting you pick day or night, fog, and even high winds! And if you feel like creating your own course, you can do so with GIMP.
If you want to try out a classic or relive some nostalgia, you can download the game from here.