SNK has released a Neo Geo controller for the Wii, and I think it looks pretty good. It's supposedly works for both Wii games and Virtual Console games. There are no details as to how it connects to the Wii that I can see, but I would guess it's either wireless or plugs into the Wii-mote. For $60 I would hope that it's stand-alone though.
For those interested you can get one here - http://www.play-asia.com/paOS-13-71-113-49-en-70-2k7a.html