Anything that's been ported to it. Depending on what the game uses, it may or may not be trivial. Oh, and it has to be open source. In short;
-The source code must be available to the public, else no port. NO EXCEPTIONS!
-Generally, anything that uses SDL is more likely to be easily ported. OpenGL, maybe, if it can be converted to OpenGLES easily.
-Nothing that relies on DirectX can be ported, for those libraries are closed-source and Windows-only.
-Nothing that relies on X86 assembler can be ported. Two different processors are in question here; square peg, round hole.
Ninjas skulk amongst us...