Attacking my first idea as a scam...

[Gilthanaz]

Just in case no one has mentioned it yet:
http://www.cnet.com/how-to/create-a-retro-game-console-with-the-raspberry-pi/

Raspberry with controller support to play all kinds of games on emulators using a controller. If you want to go really old school:

http://www.networkworld.com/community/blog/how-rig-raspberry-pi-support-nes-controllers

You can attach original NES controllers to the raspberry as well, so...

Also, i've seen one of those built into an arcade cabinet with one of the very old school control stick(s) and buttons for the super-retro arcade-hall experience.

Have fun.

Edit:
Also, you could put the whole thing into an old computer chassis and fit in some standard keyboard + PSU and you'd have your all-in-one-machine-like-that-c64-was

- G