I've got a couple of books I use:
Training Retrievers to Handle by D.L. and Ann Walters
Dogs: The Ultimate Care Guide by Prevention Pets
Dog Training My Way by Barbara Woodhouse
But I can tell you my secret and it has nothing to do with books. Take your dogs hunting, a lot. For training purposes I'll go shoot barn pigeons, rails, snipe, coots, whatever is legal, is a bird, and has a smell. Once your basic work is done it's all about cultivating that hunting skill and no back yard work can do that. A dog that has all the talent in the world that hunts 4 days a year is just a dog. A dog with average talent that hunts 25 days a year is machine.