There's just no beating the games you played so much as a kid.
I think that not only is well said, but probably enough said. And if you can't find your game on MAME, odds are it ain't emulated.
At any rate, to get to the heart of this thread, Pac-Man, Centipede, Asteroids (first arcade game I probably ever played regularly), Missle Command, Dig-Dug, et. al
Occasionally I run across some rare / strange ones that no one here in the US heard of, such as Aqua Rush...not well emulated yet, some sound issues, but man is that fun to play (think "reverse Tetris with bubbles.") Very challenging and relaxing all at the same time.