I'm into games recently and as gaming in Linux is not that good compared to Windows. But now that Steam has announced to bring their games to Linux, this might change. I've read about Wolfire's promotion regarding donating to charity and developers by giving six quality games: Aquaria, Gish, Lugaru, World of Goo, Penumbra, Overture, and Samorost 2.
Aquaria is a 2D underwater adventure game, which has good graphics and rich story, which I like despite it has been created only by two developers for two years.
Gish on the other hand is a blob of tar with unique abilities that can climb walls, slide through narrow tunnels and jump with difficulty (at first), and will make you laugh.
Lugaru is a kung-fu, ars-kicking, action-packed rabbit that at first make you wonder until the story will turn to be serious. It has high-definition graphics and will be sparring with speed.
World of Goo is a creative and very unique game, which at first try will make you think it's a game for children but it is also enjoyable and fun for teenagers and adults too.
Penumbra: Overture is really creepy. When I first tried the demo years ago, I didn't have the guts to play it because it's that scary. It has very good graphics and a unique gameplay which is not only click-and-point but you must also drag the mouse to interact with the items around you.
Samorost 2 is a flash-based game that is very creative and imaginative. The game is point-and-click but it has puzzles which is out of this world. Very enjoyable, and I recommend you to buy their latest game Machinarium.
Humble Indie Bundle is going open source, but you might still want to donate at any amount to charity and help promote cross-platform games for Linux, Windows and Mac. This promotion has limited time only.
(Update) It has only one more day left!