For main stream stuff, there are a lot of good girl groups comps that you can normally find digging through the buck bins. They usually chock full of groups like the Shangri-Las, Shirrelles, Ronettes, Crystals and Angels.... All of whom are in the same vein, but the Shirrelles and the Ronettes are my personal favorite. A lot of the motown stuff is pretty great too... The Supremes (Before Diana Ross became the vocal point), Marvelletes and Martha and The VAndellas are can't miss records.