I Wanna Be The Guy is a few years old, but looks like a very entertaining retro style indy game. I haven't played it yet, but from videos and reading about it the game seems to be pretty difficult. Looks like fun, and free to download.
Gyruss - Classic carts back to back / Mark plays.... (SD) - Gyruss is a very nice shmup that is very similar to Galaga and Galaxian only with a conical/wrapping screen lay out and some fancy emulated ' scaling' effects creating a 3D look.
Weird officially hacked version of SMB for Famicom. This one isn't fan-made; it really was released by Nintendo (I believe as a tie-in to a local famous personality at the time). Has different sprites and levels than SMB (I personally find the different sprites pretty awful looking). Very interesting as I didn't know there were a bunch of official versions of SMB until a few years ago.