The NESoid, SNESoid, and Gensoid all work great. For these, it comes down to finding good ROMs. Agreed with the above that the touch screen is a pain in the ass. As soon as I change the batteries to my Wii controller, I am going to give the Wiimote app a try. Overall, I'd give these a 4.5 star rating.
I want to try the PSXoid as well to play Final Fantasy VII, but I'll wait for the sound bugs to be worked out.