I buy charm packs. Recently I bought a few mini-charm packs (2.5" squares). I'm going to make a double Irish chain, and the 2.5" size is really nice for that. Already cut and matched -- just need to get the coordinating yardage.
I get my packs and jelly rolls from Green Fairy Quilts:
http://greenfairyquilts.com/ Good prices and incredibly fast delivery services.
Oh... and free shipping in the US, too. Every dollar saved is just that much more for fabric...