I'm a big Neo Geo fan . . . bought the home system when it first released in 1991 for like $600.00, and picked up almost all the games on home carts and MVS formats. Used to have a 4-slot cabinet, but I sold it a while ago.
Some of my top favorite games for the system are the entire Metal Slug series, the Samurai Shodown series, Last Blade 1&2, Garou: MOTW, the King of Fighters series, and the Fatal Fury series. I also love some of the shmups on the system like Alpha Mission II, Pulstar, Blazing Star, Viewpoint, and Strikers 1945 Plus. Shock Troopers is also a classic top-down soldier-based shooter, which is fantastic. There were a lot of great games released on the Neo Geo, and fortunately some of them are on PSN at least, so people can check them out on PSPs or PS3s.