Yesterday I bought my copy of the Humble Indie Bundle #4. And while the donation part is a good thing, I directed most of my payment to the developers of the games to allow them to make more games, which run natively on Linux.
I haven't played much yet (no time) and just tried out the game for which the Torrent finished first (Bit.Trip.Runner). The nice thing about that game is, it is available as a Debian package, the not-so-nice thing about said package is, that it installs stuff in places where it shouldn't and has tons of wrong file properties like ownership of the files... The Depends line is also more or less pointless, as it just lists the needed packages, but not the minimal versions. Hopefully these things will be fixed in a future package version.
Apart from that, the game in its retro look is sort of addictive. Yes, it's "just" simple Jump'n'Run, but it is a lot of fun to play. Partly because you "play" a simple melody, when you clear obstacles and collect the gold and other goodies.
Anyway, long story short, if you want a few nice DRM-free games running natively on Linux (in my case with the Mesa3D drivers for my Radeon), I can recommend this bundle. And maybe the games get open-sourced in the future as has been done previously. None of these games are so called AAA titles, but that doesn't mean they can't provide some fun hours. And to top it off you don't need Wine or something else to run them on your Linux system.