I have several that I really like, but I think if I had to pick one favorite it would be one of my Molly Katzen books - either the Moosewood Cookbook (the original one) or The Enchanted Broccoli Forest.
I like Molly Katzen, too. Her Sunlight Cafe is really good. It's breakfast recipes, and many of them make good snacks or meals at other times of day. It's helping me get out of a breakfast rut (ds just doesn't want to eat the same thing every day, so I've had to get more creative).