I'm surprised no one cooked up the idea of the Retrode 2 game adapter sooner. It's a little box that allows you to attach real Nintendo Super NES and Sega Genesis cartridges and controllers to your computer.
Once everything is hooked up, you can access the program ROM and SRAM (for game saves) on the cartridges using an emulator. A maximum of 2 Genesis and 2 SNES controllers can be connected at once -- you can even use all four controllers at the same time for some wicked multi-player action. You don't even need cartridges to play if you already have ROM images loaded onto your PC.
Retrode 2 measures 162mm x 80mm x 42mm and retails for $85. The package includes a USB cable and instruction sheet, and the manufacturer promises driverless operation under any OS with any SNES or Genesis emulator.
All in all, this is a neat emulation solution for people who don't like the idea of scouring the dark underbelly of the Internet for illicit ROM collections.