It is good to know that it's possible to play those classicNintendo NES games on any Android device with physical keyboard (Motorola Backflip, Droid, LG GW620, etc.). Thanks to the processing power of these latest mobile phones and the lesser restrictions (compared to Apple App Store) from the Android Marketplace, you can install a NES emulator app on Android. The one emulator that I can highly recommend is Nesoid.
Nesoid is filled with features and options and can run just about any NES ROMs that you would load it with. However, you will have to get your own game ROMs because it doesn't come with any. If you would like to know where to find some NES games, why don't you ask Google.
The ROMs can be stored in the SD card and can be easily loaded on Nesoid. You can access your list of games from Nesoid's simple but polished file manager. The game state can be saved even during mid-play and it can be loaded again at anytime and start where you left off.
In Nesoid, you can tweak several options like change the aspect ratio or stretch to fit the screen so it's possible to play games in full-screen mode. If you want, you can play the games at their native resolution but that would considerably reduce the playing area and would not be good for your eyes. The frame skip can also be adjusted to improve the overall performance. Enabling auto frame skip can run the games at normal or accurate speed.
Even though Nesoid has virtual on-screen keys like the start and select buttons and the d-pad, it lacks the 'A' and 'B' buttons, so you won't be able to play at all if you don’t have a physical keypad. Using the QWERTY keyboard, the default key settings are 1, A, Q, W for up, down, left, and right, O and P for the B and A buttons, and delete and enter for select and start. The buttons can be reconfigured to suit your needs.