John Shaw books are of great reading, as they tend not get too technical. Any and all of his books are great with topics from field techniques to close-up photography. Just go to my links page, you will find his site with a list of all available books.
Most of the photography magazines are useful; I tend to stick with the magazines that are specific to nature and wildlife photograph. The magazines I most read are Outdoor Photographer, Nature Photographer Outdoor & Nature Photography by Balians and Nature’s Best. You will find links to most of these magazines in my links page.