I thought about this after buying one of the NES versions of Pac-Man tonight. Here's what I have:
Pac-Man
-The awful 2600 version
-NES (unlicensed Tengen cart)
-SNES (unlockable on Pac-Man 2)
-PS1 (via Namco Museum Vol. 1)
-PS2 (via Namco Museum)
-Neo-Geo Pocket Color
-GBA (via Pac-Man Collection)
Total: 8
Ms. Pac-Man
-Genesis
-SNES (unlockable on Pac-Man 2)
-PS2 (via Namco Museum)
-Game Gear
-GBA (via Namco Museum)
Total: 5