Oh wow, I forgot a large chunk of my childhood.
POKEMANS!
I own the following versions:
Blue, Red, Yellow
Silver, Gold
Ruby
FireRed
My favorite Pokemon has to be Mew. Jesus Christ Mew is awesome. It can learn anything and still look cute.
Also, I have a limited-edition Gameboy Color that has a busted screen, but it's gold and has Pichu and Pikachu on it. I suppose it could be worth a lot if I replaced the screen.