It took me a long time to find and procure my systems. However, there are some series that there really is no replacement for. Fatal Fury, Real Bout Fatal Fury, Samurai Shodown 1, 2, 3, 4, Aero Fighters, Ghost Pilots, The Last Blade, The Last Blade 2, Ninja Masters, Bust-A-Move, and numerous others.
Bluevoodu (Dave) has some incredible deals on Neogeo CD systems. If you cannot afford a Neogeo Home Cart system, they are a cheap, affordable way to play these games.
And, I can assure you, that the CD system (though the loads are long) are graphically and gameplay wise better than any port of the same game out there.