Most of these are estimates done by memory.
Atari - 4 games
NES - 12 games
SNES - 4 games
Sega - 3 games
GB - 3 games
N64 - 8 games
GBA - 3 games
PS2 - 3 games
I'm not really too concerned when I hear people say "this system has more games", since I am usually too broke to get more than a few before the next big thing comes along
.