Have to update the list because we'll need a boxart done for Virtual Boy now too:
Colecovision: No Boxart Available, Prototypes, Homebrew
Colecovision ADAM: No Boxart Available
Game Boy: No Boxart Available, Prototypes, Unlicensed
Game Boy Color: No Boxart Available, Unlicensed, Prototypes, Pirate, Homebrew
Game Boy Advance: Unlicensed, Prototypes, Pirate, Homebrew, Special Releases (See Above)
Game Gear (Alternate Box, See Above): Prototype, No Boxart Available
Virtual Boy: Homebrew
Watara Supervision: No Boxart Available
EDIT: I added the colecovision and ADAM entries above after making the post originally.
EDIT2: Hey Gilles.... What do you think about making a boxart of your own with the Pokemon Mini on it that will be the boxart for all 8 games? It's completely your own creation man. Whatever you want it to look like will be perfect.
I was thinking we could do the same thing with Chip8, since there obviously isn't any boxarts for Chip8 games.