In reply to Jay218: "On Rope" (I can look up the author and publisher, if you need, but that's the exact title) is considered by many cavers to be the Freedom of the Hills for ropework. Not just knots, lots of other stuff. Heavy, perhaps a bit pricey, but you get what you pay for with it.
Falcon publishes a few paper-backs (Climbing Anchors, More Climbing Anchors, Climbing Knots, and maybe a couple others) that look like you get more than you pay for. Outside shops generally seem to carry them - probably most better-stocked shops would have some.
Perhaps also google for rescue ropework, or join a SAR team that is technically-oriented (e.g. my old team had something like 30 knots, bends, and wraps in their personal-ropework assessment!)
