Don't forget the Cuttle Cart II, that's the most amazing one of them all in my opinion. The entire Atari 2600 and Atari 7800 library with POKEY sound for the 7800 releases that utilize it, 7800 high score save support, 2600 Supercharger support, etc. Basically, everything except Pitfall II works on it.
Adding new games to it is a pain though, wish all that was more simpler like some of these more recent ones.