A Raspberry Pi can be setup to run as an emulator all the way up to PS1 games. So if you buy a cheap Pi
http://www.memoryexpress.com/Products/MX61462
Then just put an image on the flash card and use a controller like PS3 wired or wireless with a Bluetooth adapter.
http://www.emulationstation.org/gettingstarted.html
The basics but if you want an all in 1 HDMI solution with crisp graphics you can't go wrong with Pi.