With all the C/Python/SDL-based libraries mentioned here, I’d like to advertise my/our gamedev library, Gosu. It has originally been my private library, spread only via ICQ/IRC to interested people, until I made it public to use it for my LD3. That is a while ago, and in the meantime, it has been used for some LD entries by me and other people, also for more serious projects, and is actually documented.
Long story short, Gosu is a 2D game development library for Ruby and C++. I guess the C++ version is a bit too heavy to learn until Friday *and* actually use, though. The Ruby version gets you up and running quickly.
Pro (compared to your generic SDL wrapper): *Very* fast graphics with rotations and all that, because the library was designed to use OpenGL; an API which tries not to get in your creativity’s way; examples on how to integrate it with ImageMagick and the Chipmunk physics library; serious OS X support.
Contra: Linux port misses gamepad support; can’t handle too complex text input well.
If you would like to give it a try, the library can be found at http://code.google.com/p/gosu.