Unreal Development Kit http://www.udk.com/download
XNA Game Studio Express (DirectX and C#)
Download: http://msdn2.microsoft.com/en-us/xna/default.aspx
Forums: http://forums.xna.com/ Starter kits: http://creators.xna.com/Education/StarterKits.aspx#ShipGame
OpenGL C/C++
Tutorials: http://nehe.gamedev.net/
Forum: http://www.gamedev.net/community/forums/forum.asp?forum_id=27&forum_title=NeHe+Productions
OpenGL.org Forum: http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=cfrm
FAQs: http://www.opengl.org/resources/faq/
DirectX C++
Tutorials: http://www.riaz.de/tutorials/d3d.html
Forum: http://www.gamedev.net/community/forums/forum.asp?forum_id=10
Forum: http://forums.xna.com/
Any bare bones 2D API
Example: Gtk: http://www.gtk.org/
Java3D
Download: https://java3d.dev.java.net/
MASON Multiagent Simulator (in Java) Download
Unity Engine Download
Game Engine Databases - Include Linux sections
http://www.devmaster.net/engines/
http://cg.cs.tu-berlin.de/~ki/engines.html
Irrlicht Free Open Source 3D Engine
http://irrlicht.sourceforge.net/
DarkGDK (high-level game-specific engine)