The launch of The Humble Double Fine Bundle means that for a limited time you can get Psychonauts for the low price of whatever you want. You'd be a psycho not to take that offer!
I'm so sorry about that, but it's true. And for whatever price you choose, you'll also get Costume Quest and Stacking. Pay more than the average ($8.29 at the time of writing) however, and Double Fine will throw in an extra umlaut in the form of Brütal Legend.
Pay $35 or more, and you'll get all the games plus a "slacker backer" pre-order of Double Fine's Kickstarted adventure game, Broken Age. The post-Kickstarter backing program grants you the following:
Access to making-of documentary episodes in HD
Access to private forums featuring concept art, development updates, team and backer discussions
Participation in the closed beta
A Steam code for the finished game on PC & Mac, or a DRM-free download on PC, Mac, or Linux
The bundle also features the Psychonauts and Brütal Legend soundtracks, and all games are available on Steam or as DRM-free downloads for Windows, Mac, and Linux. As always with Humble Bundles, you can partition your contribution any way you like to support Double Fine, charities, and the organizers, Humble Bundle, Inc.
Oh, and for a less-humble contribution—$75—you'll also get a classy Double Fine t-shirt. Unfortunately, the shirt is not available as a download, but worldwide shipping is included.