GameBase (http://www.bu22.com/) is a collection of databases containing info, screenshots, music, sometimes ROMs, and other data, each for a specific system. Some of the GameBases are not directly downloadable, since they contain ROMs. They used to be available on underground-gamer.com, but it was taken down, and now they can be found on their forums, and sometimes on torrents.
It's really not a professional database, and has many inconsistencies, it's not properly normalized, and the data is sketchy sometimes.
Vampi has managed to import all the gamebases he could find into mysql, and made it browsable here.
|Sinclair ZX Spectrum||SpeccyMania||World Of Spectrum|
|Sharp X68000||X68||Games Database|