No arcade machine is complete without a lit display on the top and a sound system worthy of transmitting the bloops and bleeps of classic arcade games. While you really want the graphics and controls to feel authentic, it's the little touches that help complete the feeling of playing on an actual arcade machine.
For the arcade machine's overhead display, you'll need a light source, some plexiglass and a marquee, which is a translucent material with artwork on it. If you don't have the ability to make your own marquee, you can buy one. Several Web sites sell marquees for MAME machines and can cut the material to whatever size you need. Many even offer designs that incorporate the MAME acronym into the artwork. Some also offer graphics you can mount on the side of your arcade cabinet.
Fluorescent light fixtures are good light sources. They don't generate a lot of heat, the bulbs last longer than incandescent lights and you can find the bulbs and fixtures in different lengths.
You'll need to sandwich the marquee between the sheets of Plexiglas to protect the artwork. Install the fluorescent light in the top of the cabinet and make sure the light source is aimed toward the front of the cabinet where the marquee will be. Test it out to make sure you've got the effect you wanted -- you can make tweaks by either moving the light source closer to or further from the marquee or by using a different bulb wattage.
As for sound, that depends on what you're using as a monitor. If you're using a television set, the set's speakers should work fine. But if you've chosen to go with a computer monitor, you'll need to install a sound card in your computer, and mount some speakers inside the cabinet. You'll also need to make sure the sound card is compatible with the version of MAME you'll be using. It's a good idea to shop around for speakers since you'll want something that can recreate the entire range of sounds you'd find in arcade games. You may also want to mount the speakers near the marquee if you want to avoid a muffled sound.