I have acquired rather a lot of vegetarian cook books over the years! One of the best that I've got for simplicity, variety and practicality is this one:

Vegetarian Cooking for Everyone
I bought my copy second-hand, but it'd be worth it new. Pity it doesn't have many photo's though.

Otherwise, this was a recent gift to me. And it's an amazing piece of work for history, culture, geographic scale, everything.
Veering a tad off topic perhaps, but for anyone interested:

Olive Trees and Honey: A Treasury of Vegetarian Recipes from Jewish Communities Around the World
A sort of curl up in an armchair for the afternoon with a couple of glasses of wine and fantasise book..