Im assuming you know of Star roms. 100+
Then there is the capcom cd set that hotrod sells.
Then there are the game packs. Not as 'legal' but good enought for most.
Next...
All of these are licensed for individual/personal use only. If you really want legal roms for a real machine.... finding dead boards on ebay is probably your best. (but even then, its in question... but with the new law allowing emulation on systems that are not commercially available it should be fine)