Simple DirectMedia Library
The Simple DirectMedia Library is a cross-platform C library for dealing with graphics, sound, joystick and keyboard/mouse input. It provides a nice, if rather simple, API for setting video modes and drawing graphics, and has some OpenGL support. This is great stuff for writing games.
Currently, Neil Madden is working on a simple binding of SDL for Tcl. This will be pretty much a direct mapping of the SDL API to Tcl (but following Tcl's conventions). This will be mostly useful for scripting SDL components written in C, but you could write stuff in Tcl if you can live with the performance hit, or for prototyping.
Kristoffer Lawson is working on a higher level binding for Tcl, called Oil, which is directed at games and other multimedia presentations, that are scripted in Tcl.
There is a certain amount of overlap in these projects and hopefully effort can be made to merge parts.
Other media libraries it would be nice to have in Tcl:
OpenAL - a 3D sound library, useful for effects. I don't think Snack has spatial sound.
What about Kent Mein's TclDemo at http://www.libsdl.org/projects/tcl-demo/ ?
Jim has some SDL and SDL_Glx binding in the current distribution. Check Jim Extensions for example and screenshot.
Tcl3D wraps the Audio and CD related portions of the SDL library. It also has some demonstration programs using SDL.