Using controllers in other consoles.

[retrolinkx]

I think this is somewhat well know, but did you know the Atari Controller can be fit into a Sega Genesis/Mega Drive controller port?

It also works the other way around, the Mega Drive controller can be used in an Atari controller.

They work too.

Edit: Master system controllers work as well.

[JonathanPonikvar]

This trick also works with the old ColecoVision console. All of the above controllers can be plugged in to work with any game on the system. My grandmother had both a Coleco and a Genesis, so I found this out as a kid when I realized the plugs on the controllers were the same. Pretty cool little trick, although since the Coleco pads also had a full numeric keypad (with those annoying plastic inserts for each game), certain titles were limited in compatibility.

And trying to play Sonic with one of those clunky Coleco controllers? Now THERE was a challenge mode.