Dig Dug is a really great port. I also like Asteroids, Jungle Hunt, Berserk and, of course, Centipede. Okay, Centipede's graphics are very "basic", but it has the great gameplay of the arcade.
Don't forget Kangaroo. It's fun to play and has all the things from the arcade: different fruits, the bell and monkeys throwing apples. You also have 3 different screens, which are really challenging.