Trying my best to ignore everything between the first post and this one.

Although I have a dedicated vertical 4-way machine, my upright horizontal 6-button 8-way cab has MAME, NES, Sega Genesis, Atari 2600, Atari 800, and Playstation One emulators set up. Mame gets a lot of play, but there are also quite a few quick pick up and go games on the consoles that are big hits with visitors and also my kids. Many are 2-player simultaneous games. I try to keep the game list small on each, avoiding games that need instruction manuals, are heavy on the time investment, or have counter-intuitive controls. It does take some time to get the emulators setup properly, but I'm glad I did.
PSX - Twisted Metal 2, Tekken 3, Unholy War, Poy Poy, Tekken 3, Crash Team Racing, and Star Gladiator are favorites with my boys.
NES - Pro Wrestling, Excite Bike, Super Mario 3
Atari 8-bit - Archon, Blue Max, Crossfire, Alley Cat, Seawolf 2, One on One, Matchboxes (favorite of 7-year old twins), Dog Daze Deluxe, Kikstart, Missile Command
Sega Genesis - Zombies Ate My Neighbors, Toe Jam and Earl
Atari 2600 - Fishing Derby, Freeway, Bowling, Frogs n Flies