I just bought a copy of this book (written by Elizabeth Schneider) and feel compelled to recommend it to anyone interested in the subject. I'd guess there are entries on at least 200 vegetables (the jacket says 275 photos and 500 recipes, but most vegetables merit several recipes and some have more than one photo). Each entry contains at least one color photo, info on alternate names, cultivation, traditional uses and history, as well as choosing, storing and preparing the vegetable. Then come a few recipes (most of which seem pretty easy to prepare) and a separate section titled "Pros Propose" -- a compilation of ideas and tips from various professional chefs. It's an awe-inspiring volume and has got me dying to run out to the farmers market tomorrow to track some of these vegetables to try.
It has a couple of minor drawbacks -- the author explains that she has skipped the "well known" vegetables if she felt she didn't have anything fresh to add about them. So there are no entries for tomatoes or bell peppers, for instance, and the potato entry is limited to some of the "newer" varieties like fingerlings and the colored potatoes. No entry for chiles of any kind, because she considers them primarily a spice rather than a vegetable. But one can't have everything, I guess.
At $60, it's not cheap, but if you like vegetables, or don't like them but feel compelled to try to eat more of them, or want to expand your vegetable repertoire, or simply want to know what purslane looks like, you have to buy this book. As an added bonus, if you buy it through the Chowhound Amazon link, you'll be supporting this site as well.