Various commercial game engines are starting to emerge as standards, used either by professionals or amateurs.
There's a Wikiwiki page dedicated to the Unreal engine:
If you like to make little puzzle games, or want to see an object oriented ArtWare system done right, check out GameMaker.
- Axiom - C# port of the Ogre game engine (http://axiomengine.sourceforge.net/).
- Crystal Space - http://crystal.sourceforge.net/tikiwiki/tiki-index.php?page=About+Crystal+Space
- 3D Game Studio - http://www.conitec.com/
- BlitzBasic - http://www.blitzbasic.com/
- DarkBasic - http://www.darkbasic.com/
- JaMagic, MultiMediaFusion, TheGamesFactory - http://www.clickteam.com/