Don't forget the NeoGeo CD. Boots CD-Rs just fine.
IIRC, the Dreamcast isn't totally "unmodified". You can't just boot a copied game, you need either a mod, a boot disc, or a modified game. (Don't remember the specifics, but I still have my cheap mod around here somewhere... I ordered it when it first came out, but by the time I could get around to installing it the boot discs were out, and soon after that pre-patched images too...)