Forget emulators -- if you've got a smartphone, the Atari iPhone App is the perfect option for retro gaming.
The Atari iPhone App brings back a bunch of old-school classics without the hassle of downloading emulators online. The games are as legit as possible, retaining the same graphics, controls and concept. The only obvious difference is that you're playing on your mobile instead of in front of the TV on the console. The app is packed with classics such as Pong, Missile Command and Yar's Revenge.
If you want to get away from the hectic nature of Left 4 Dead and want some good ol' simple gaming, the Atari iPhone App is for you. It's currently available for purchase at the iTunes App Store.