Look for sets using .chd (Compressed Hunks of Data) for disc games or .7z for cartridge games to save significant space without losing quality. How to Find ROM Sets
It is important to remember that downloading ROMs for games you do not own is technically a violation of copyright law in most regions. download complete rom sets
Usenet is a paid service ($10/month) but offers insane retention rates and DMCA resistance. Look for sets using