Personally, I would love to see a 360 light-gun. That gun thingy that was supposed to be used with Gunvalkyrie would be awesome to own as well. There's something about light-guns. I loved how the Time Crisis games came with their own cardboard boxes. (A trend that I miss in PC gaming, BTW.) What about you guys?
A vibrating ring (with a cumbag on its base) which plugs in ps2's memory socket for extra pleasure while playing Rez.
Quality wireless controllers for the older generation systems. An idea which didn't really come into its own until quite recently.