I have two in my collection:
Meat Free Monday Cookbook - It has great recipe ideas for all meals (the "packed lunch" is nice I find) and gorgeous photos. It is also divided by season, which I find nice as a reference before I head down to the farmer's market.
Simply Satisfying - by Jeanne Lemlin. This is more of a traditional cookbook set up, but with a vegetarian focus. It has a wide variety of cuisine styles (just look at the table of contents on the Amazon preview), as well as having a "menu" section in the back that pairs different recipes in the book together so you can have a focused meal plan.