If you look in the crochet pattern books in your local store, there are some great patterns for afghans that are made up of a bunch of different squares. There is a pattern that I have in particular, where each square in the blanket is in a different "stitch" such as single crochet, double crochet, triple crochet, popcorn stitch, etc. The pattern made them all out of one or two colors, and then used a plain color like white/ivory to edge them and attach them all, and do a nice edging. But, to use leftovers, you could make each square from a leftover fabric instead. It would make one of those great, homey throws that are great for watching a movie on the couch with.