I started tracking down The Complete Motown Singles box sets, and my god, they are unbelievable.
I grew up on Motown, but I had no idea how much solid gold this company cranked out every year. The link above is just to the first volume. They'll eventually have 12 volumes (each around 5 discs, and each disc around 25 tracks) that collects all the A and B side singles they released between 1959 and 1972...
I've only loaded the first three volumes onto my computer, and I'm already up to 384 songs!
It's a staggering amount of music, and nearly all of it is incredibly good. If I could build the soundtrack to my films from any music catalogue, it would be Motown.