Some Official and Unofficial Developer and Flash Cartridges

official nintendo flash cart: scans - reverse engineering

official test cartridge: chipmusic post & handheldmuseum & youtube video

EEPROM development cartridge: handheldmuseum

DIY cartridges from reinerziegler.de

PLCC ROM cartridge: digital-circuitry.com/GameBoy - youtube howto

MBC5 simulation with a CPLD chip by xzakox & wiki notes

Gameboy Uber Cart (FPGA based): robotdungeon

MBC5/CPLD home1.stofanet.dk

devcart by drakon

Youtube videos showing these carts:

• https://www.youtube.com/watch?v=jwPO1nyyQbk
• http://www.youtube.com/watch?v=1cbdZjozn54
• https://www.youtube.com/watch?v=L_ijZM-Ic4c 
• https://www.youtube.com/watch?v=EYNWKxO9VQ4

Extra links:

• chipmusic - photos of gameboy flash cartridges
• http://zdoom.ic.cz/gameboy.html 
• http://www.flickr.com/photos/ableeplife/with/2785239493/ 
• https://www.youtube.com/watch?v=VX9_nvVSxx0  of the nintendo EEPROM cart