I found some really cool source patches for Blender. I think a few are even for the game engine :D. It is definitely worth a look.
I read the first page and only the first one would be useful in the game engine, I noticed all that’s listed is from Broken, who doesn’t develop the game engine.
Here is another site with some patches. Some are even compiled. (I’m not sure if they are relate to the BGE though).
Most, if not all, is not for the game engine, note that most of the developers are developing the modeling, texturing, animation, and rendering areas, not for the GE.