I've decided to put my collection of official DS Download demos online. It is the most complete collection online that I am aware of, please let me know if I am missing any. The only other large collection I know of is at sgstair's wiki, and it is missing a bunch of the newer ones. I've made a php script which will automatically pull out the icons and file info directly from the .nds file. Now if only I knew how to design webpages, I'd make it look nice, but it's functional enough for now.

Legal disclaimer: I am putting these online in good faith that Nintendo and the respective copyright holders wish them to be distributed, as they are only demos, and are not (and have never been) sold anywhere.

Well, these roms have the .nds extension, which most recent flashcarts and memory card adapters are compatible with. I'm not too familiar with the GBAMP. What file extension do you usually use with that?