I'm a novice fly-tier and have purchased a few books and have a website reference I used (and still use) a lot when I first started tying.
As Jason suggested, "Trout Flies" by Dave Hughes and "Fly-Fishing Pressured Water: Tying Tactics For Today's Trout" by Lloyd Gonzales are both excellent references (Jason - thanks for the suggestion on Lloyd's book). The former provides a number of practical recipes with step-by-step instructions and close to one hundred variations to match most any insect you might encounter on the water. The latter of the two provides some VERY realistic patterns - realistic enough to mistake for the finished products for the real thing. I'm not quite at the level I need to be to do the recipes justice, but even as a novice, I feel pretty confident about tying these flies in the near future.
One reference I swore by for a bit was "The Benchside Introduction to Fly Tying" by Leeson and Schollmeyer. I actually received both this book and "The Fly Tier's Benchside Reference" for Christmas, and both have served me well. "The Benchside Introduction to Fly Tying" is set up in a sort of "split-screen" fashion in that the recipes and some step-by-step instructions are on the top half of the book and detailed techniques are on the bottom half - most of the basic fly recipes and basic techniques are found in this book, and I feel that this one book will get you very far in your fly-tying "career." "The Fly Tier's Benchside Reference" is also an excellent reference, with every technique you could possibly imagine described VERY thoroughly, with excellent pictures. Something worth noting, however, is that "The Fly Tier's Benchside Reference" has NO fly recipes. I would certainly still purchase the book, but do not expect actual recipes.
Finally, a website I found very helpful was www.flyanglersonline.com. On the left hand side, click the "Fly Tying" link, and go from there. There is essentially a how-to on everything from materials to recipes - they have essentially set up an online course you can follow, starting with basic patterns and moving on to more advanced patterns. I've found it particularly helpful in case a picture didn't make sense in one of my other references. Anyway, sorry for the not-so-brief post, but hopefully this helps some. Good luck.
P.S. I know our TU chapter (Ithaca area) holds an annual fly-tying workshop in the winter, so that might be somewhere else you could look. Cornell also offers a fly-fishing class which includes fly-tying, so you might check with the college(s) in your area as well.