clodev,

As mcsteff mentioned the fly tying section on FAOL is invaluable, and free. I also like westfly.com (entomology section). I have both Trout Flies and Fly Tiers Benchside Reference, and the later is much more about tying techniques than pattern recipes. I am glad to have both. I also like Randall Kaufmann's Tying Dry Flies and Tying Nymphs.