I use the Stoke's Guide for the Western Region which should have most of the birds you will find from Central Kansas to the Pacific Coast and Alaska. In my experience, the more specific guides (like "Birds of Colorado" or "California" etc...) are usually pretty lacking and leave you scratching your head a lot.

That's perfect, and thanks for the tip!

No problem. There's several good ones. I like Stokes because it has multiple photographs of each bird. Audubon field guides are decent, but not my favorite, because you have to back reference between picture and information and there's only one picture of each bird... well take red-tailed hawks for example, which have a huge variety of color morphs so you need multiple pictures. Sibley's is another very good one, but I prefer photographs to drawings is the only reason I don't use that one.