5. World Karate Championship A.K.A International Karate
I'm not a huge fighting game fan, but I find this game really fun to play in both the 1 player and 2 player mode.
4. Gyruss
A really accurate port of an arcade classic, Parker Brothers really knew what they were doing when programming this port.
3. Boulder Dash
An addictive action puzzle game by First Star Software and a really good one at that.
2. Jumpman
A really good arcade style platformer for the C64.
1. Bubble Bobble
I'm so glad I got an NTSC copy of this game, because it ended up being my all-time favorite C64 game as of now.
Honorable Mentions:
Gridrunner
A really good fast paced Centipede-like game by Jeff Minter.
Speed Buggy
one of the first games I got for the C64. A good port of a good racing game.