The Bittman book is excellent--lots of simple recipes and tons of modifications/variations, so you can go fairly basic or get exotic and try out new ingredients. I also like all of the Moosewood cookbooks, but particularly the original one and The Enchanted Broccoli Forest. There are also a lot of fantastic websites/blogs. Heidi Swanson's 101 Cookbooks site has a ton of recipes; we have several in our regular rotation and I have yet to find one that hasn't been good. Our library has quite a few veg cookbooks in their e-books catalog, as well as print copies, so you might also check out a few of those before you commit to anything. Have fun!
