Even though it's totally old now and its games are ported everywhere, the Neo Geo still seems like a special, vaguely magical system -- probably because of the price. It doesn't seem like the DS should be powerful enough to run its games, but homebrewer Ben Ingram has proven that it is possible with NeoDS, a Neo Geo AES/MVS emulator.
Full sound emulation and (most importantly) multiplayer have yet to be implemented, but according to DCEmu, "Games like WindJammers, Metal Slug and Fatal Fury work either perfect or near perfect." Soon you'll be able to compare Metal Slug 7 to its predecessors on the same screen! If you own them, that is. Don't be a pirate.
[Via DCEmu; thanks to everyone who sent this in!]