Found this via the roundabout route of 8bitRocket and Rich's site at photonStorm.

Mame has been ported to Flash. The daddy of all emulators is running with a healthy list of games. They lack sound, but that's always going to be the way as Flash's sound control is just one step up on a Spectrums, but it's not the end of the world ( For all the rose tinted spectacles in the world, arcade sound was never that great. Apart from Defender of course ).

Please please check out FMame and be blown away playing Commando ( Not a port, actual real 100% the same Commando ) in your browser.

Sex.

Squize.