The one drawback of Gibbons's books are the images, which are nice line drawings but are not overly helpful for the beginner. A modern forager, Samuel Thayer, has done an excellent job with the images in his self-published Nature's Garden.
This is Thayer's second self-published book, and it is the better of the two in my view. His first has a tone to it that put me off: he correctly points out that many foraging books perpetuate myths about plants because the authors have not actually seen or eaten some of the plants, but he cops a "they're all idiots" attitude in his first book I found off-putting. Thankfully, that 'tude is largely absent from his second book.
Nature's Garden is an excellent book if you live east of the Great Plains. Although there are a number of plants he discusses that also live in the West, more than half either do not or are so rare as to be pretty much unforagable. Still, for those plants Thayer writes about that do live in abundance here in California, I find his entries very thorough.
For those who live West of the Great Plains, there are three books I find invaluable. First and foremost is Charlotte Bringle Clarke's Edible and Useful Plants of California. Her book covers a lot of ground and is not as thorough as Gibbons or Thayer, but she deals with pretty much everything I see around me in California—and that comprehensiveness is valuable. I use this book, which has good pictures, as a stepping stone for further research into individual plants.
California, however, is an odd place (in more ways than one), and its flora is often unique. But head east into the Rocky Mountains, and there is an excellent guide, Edible Native Plants of the Rocky Mountains, which has some of the best botanical illustrations I've ever seen in an edible plant book. Many of the plants described also live in California, and each account is far more thorough than in Clarke's book. What's more, the Rocky Mountain book is written by scientists who ate everything they write about and did experiments on the edibility in various preparations. If you live between Colorado and the Pacific, you should get this book.
If you live further south, however, in the desert regions of California, Arizona, New Mexico, or Texas, you will love Gary Paul Nabhan's Gathering the Desert, which is a little woo-woo-juju concerning the Indians who developed all the uses for these desert plants, but which contains all sorts of useful information. Its drawback? It deals only with a few edible plants. It's success? It deals with those plants comprehensively.
I am heading to Massachusetts soon to see my mother and sister—and to go on one last foraging trip before my book is due in August. I know a lot of those plants by heart, but I have not lived in the East since 2001, so I looked for a New England-specific plant guide, and I found one in Russ Cohen's Wild Plants I Have Known ... and Eaten. Again, Cohen has what I view as the magic ingredient for a successful foraging book—he has actually eaten everything he writes about.