I like the Better Homes and Gardens "501 Quilt Blocks" best of all, just because it has such a great variety of blocks. I've used Georgia Bonesteel's "Lap Quilting" a lot, just for the block patterns, and now that I'm hand quilting, it's useful all over again.
Third place may belong to "The Essential Sampler Quilt Book" by Lynne Edwards. I haven't made anything out of it yet, just got it, but it has good instructions for blocks that use close to 40 techniques.
I love to do samplers, so anything that has a lot of blocks is going to be something I like. :)