nitro2k01 has made a new forum for Development for the original Gameboy, heres his news:

Hello and welcome to the Gameboy Development Forum. This is a forum dedicated to discussions about game and software development for the old-school Gameboy models, the so called GB-Z80 models. This includes the original Gameboy (DMG), Gameboy Pocket, Super Gameboy and Gameboy Color. I've been thinking about starting a forum like this for a while, but never got about doing it until the question was raised over at 8bc.
There are some discussion boards and mailing lists on the topic, but my impression is that they are all pretty dead. I believe that those who engaged in GB development a couple of years ago have moved along in life. My hope is rather to spark some new interest to the scene. I don't think this is unrealistic since I think there might be some new born interest because of the chip music revolution that has taken place the last 10 years or so.
Since this forum was created in 2008 it won't lack moderation, at least for a few years. So do register if you're interested in Gameboy software development.