Original series

-Megaman (NES, PC)

-Megaman 2 (NES)

-Megaman 3 (NES, PC)

-Megaman 4 (NES)

-Megaman 5 (NES)

-Megaman 6 (NES)

-Megaman 7 (SNES)

-Megaman 8 (PS1, Saturn)

-Megaman & Bass/ Rockman & Forte (SNES, GBA, WS)(Not Megaman 9...This can be proven if you wanna get techinical)

 

Megaman X series

-Megaman X (SNES, PC)

-Megaman X2 (SNES)

-Megaman X3 SNES, PS1, Saturn, PC)

-Megaman X4 (PS1, Saturn)

-Megaman X5 (PS1 ,PC)

-Megaman X6 (PS1)

-Megaman X7 (PS2, Not released until November)

 

Megaman X gameboy series

-Megaman Xtreme (GBC)

-Megaman Xtreme2 (GBC)

 

Zero Series

-Megaman Zero (GBA)

-Megaman Zero 2 (GBA, Not released yet)

 

Gameboy games

-Megaman (GB)

-Megaman 2 (GB)

-Megaman 3 (GB)

-Megaman 4 (GB)

-Megaman 5 (SGB)

 

Legend series

-Megaman Legends (PS1, N64)

-Megaman Legends 2 (PS1)

-Misadventures of Tron Bonne (PS1)

 

Battle Network series

-Megaman Battle Network (GBA)

-Megaman Battle Network 2 (GBA)

-Megaman Battle Network 3 Blue/White versions (GBA)

-Megaman Network Transmission (GCN)

 

Complete Works series

-Megaman (PS1)

-Megaman 2 (PS1)

-Megaman 3 (PS1)

-Megaman 4 (PS1)

-Megaman 5 (PS1)

-Megaman 6 (PS1)

 

Spin offs and Appearances

-Megaman Soccer (SNES)

-Megaman: Wily Wars (Genesis)

-Megaman: The Power Fighters (Arcade)

-Megaman 2: The Power Battle (Arcade)

-Marvel VS. Capcom 1 & 2 (PS1, Dreamcast, PS2)

-Capcom VS. SNK 1 & 2 (PS1, Dreamcast, PS2)

-Super Adventure Rockman (PS1)

-Rockboard (NES)

-Rockman Battle & Chase (PS1)

-Megaman (GG)

 

I think thats all of them to date...