Brewing Classic Styles has been great for me in learning how to put together a recipe for various styles in a "hands-on" way. A lot will recommend Designing Great Beers but I've found it to be rather dry and I don't refer to it very much. I have learned some stuff from it though. The forums here are, of course, great and I go back to Palmer's How To Brew time and time again. The thing that has really helped me lately is buying Beersmith 2. I'm still figuring it out but since I got it, every batch has hit the numbers perfectly. And now that I said that, I'm sure the batch I'm brewing today will be way off, haha.