You may also want to try artwork_crop, which only shows the part of the bezel that would be included in the main display. Thus, it pretty much just fills in the side portions on vertical games, or parts of the bezel that may overhang the screen like in Asteroids.
Asteroids, in fact, is a great example. Try it normally, with artwork_crop, with bezels disabled, and with artwork disabled and see which of the four you like best.
--Chris