CDi, 3DO, VirtualBoy, N64, Jaguar CD console, Nuon, Dreamcast, GC, gamecom handheld, R-Zone, Action Max
I want the GC emulated just for the sake of it being emulated. There isn't anything impressive enough on the GC to justify emulation of it though.
Some simulators I would like to see would be of Mattel's Classic Football, the Zelda Game Watch, and the Zelda Dual Screen Game&Watch.
Neo Geo pocket 100% emulation unless it has already happened
In the way of arcade games I currently can only think of The Ocean Hunter: The Seven Seas Adventure(Sega), Mocap Boxing(Konami), Jambo! Safari, and Radiant Silvergun.
I almost forgot DieHard Arcade.
I don't remember ever playing it but I might have once. I got to see it alot when checking out at my local Walmart years ago. It may have been ported to the PSX and Saturn.
I would like to see NES Mapper 64 emulation.
I was recently reminded of this when talking about Skull&Crossbones with someone.