Hawks in Flight: If you are a hawk enthusiast as I am, you've definitely scored if you found this one Illustrations by David Sibley, author of the Sibley guide, this book explains how to tell the difference between flying raptors. With detailed explanations and meticulously painted portraits of each raptor, This book really is one you should check out. (Pete Dunne, David Sibley and Clay Sutton)
Birding In Illinois: If you live in Illinois, this is a really good reference. It's none too durable (my copy's protective layer on the front is peeling), but is perfect as another home bird book. It gives very comprehensive descriptions of birds, shows detailed pictures, and even has a checklist in the back - If you're a kid birder, you should go with this one as a starter.
Old/antique bird books: Antique books are gorgeous, even if the cover is ripped off and the pages might be falling out. If you can find an old book like a 1940's Peterson or a 30's Golden guide, I can tell you that flipping those old-smelling pages is one of the funnest things you can do with a bird book. It's also really cool to see what they pictured the birds as, where they found them, and what they called them I have a few, and let me tell you: This is something you want to look for. And what if you don't want to keep them? Sell them on eBay, if they're in good condition. I've never done this, but some birders and book enthusiasts will pay big bucks for those things.