Gaming Workshop

Free 3D modeller/renderer with built-in games engine. Scripting happens in Python, or using a visual interface.

http://www.blender3d.com

PyGame

Gaming API for Python. No graphical tools, just source code. Allow access to SDL and OpenGL.

http://www.pygame.org/

Panda3D

3D engine with built-in scripting possibilities. Several steps up from PyGame. Made by Disney and the Carnegie Mellon Entertainment Technology Center

http://www.panda3d.org