Available on the DigitPress froums is a Pokemon Deoxys Distribution download cartridge, which was used for two weekends only as an in-store promotional cartridge.
Link (I beleive registration is required)
NES NWC Repo (CTCW)
Hotel Mario for the CD-I sealed (CTCW)
Lot Of 8 Atari Superhcarger Games – The Starpath Supercharger was an add-on for the 2600 that expanded the machines capabilities by adding additional RAM, allowing for higher resolution graphics and larger games, and by providing a connector to which a regular cassette player could be connected, thus permitting larger games, stored on tape, to be loaded. The Supercharger was connected to the Atari’s cartridge slot.
Lastly, there’s been a ROM release of a Atari 2600 Mega Man demo featuring four stages and a boss battle at the end. Check the thread on AtariAge.