MicroMario is a little platform game with 16 levels and is less then 30k.
The game runs on the standard NXT firmware and is programmed in NBC. It uses custom graphics code with a double buffer, horizontal and vertical scrolling, and XOR sprites... Everything is compiled into one single file.
If you're interested then you can download the source code here. The zip also contains the compiled version of the game so you can just upload the .rxe file.