Some years ago I decided to eat less meat and to successively becoming a vegetarian. I haven't learnt any particular dishes though, mostly just improvising with veggies/beans/nuts/cheese as staples – and that's fine, but I would now like to have some new inspiration from a good vegetarian cookbook (meaning less animal products is preferred, but dairy products and eggs is ok).
To make this question possible to answer, this is what I'm looking for:
A sort of a vegetarian's bible. Doesn't have to be very new, I'm thinking bible like Julia Childs' Mastering the Art of French Cooking. Should be very comprehensive.
Should have some dishes that are quick to make and some that are slow cooking.
The dishes should be something you can eat on a regular weekday. Some special ingredients can be hard to find or be a bit expensive, but the staples should be quite cheap and easy to get (I live in Sweden, but have Asian and Middle Eastern food stores nearby).
The recipes should try to follow the (Swedish/European) season if possible.
The cookbook can very well be of Indian cuisine (I hear they like their vegetarian dishes), so some ingredients have to be imported in that case of course.
Language: English or Swedish.
I'd recommend Mark Bittman's "How to Cook Everything Vegetarian", I use it all the time. It's certainly what I would call comprehensive; besides containing tons of recipes for everything from entrees to breads to soups, the sections are prefaced with tips on how to improvise or switch up the recipes as desired, including vegan alternatives.
The Moosewood Cookbook, by Mollie Katzen, is often regarded as a sort of bible of vegetarian cooking. It's one of the best-selling cookbooks ever, not just among vegetarian cookbooks, and helped show Americans that they didn't always need meat to make good food. The original is from 1977 and may be harder to find, but there's a revised version, The New Moosewood Cookbook. The recipes are generally pretty simple, amenable to substitutions and alternate versions, and the style is very friendly. It should have things for every season - she wrote the original while at the Moosewood Restaurant, whose menu changes daily based on what's available. The author has plenty of recipes on her website, which should give you a good idea of the style and types of recipes. If you like it, she's written several other cookbooks as well!
Note: As lemontwist points out, there's fish in some of her books. But there's plenty even without those recipes; just think of it as some added stuff you'll never make if you're actually vegetarian.
I would say that Madhur Jaffrey's World Vegetarian, with 650+ recipes, has been a source of great inspiration for me. It's comprehensive and boasts a great number of different styles and ingredients.
Additionally it's informative, offering a lot of history about the foods, the places they have come from and the people who developed them. It strengthens the "I want to go [more] meatless" mindset for everyone I've ever spoken with.
Not to mention she has won a number of James Beard Awards and she is Indian, giving her some great insight into that particular culture.
The book itself is fairly inexpensive over at Amazon too. Good luck!
Bittman's How to Cook Everything Veg I second. He's very good at explaining the basics and rarely disappoints. I'd also have to add in the "must have" category, Sundays at Moosewood, which is a collection of international veg recipes, some of which are delicious--African Groundnut Stew over millet... Sounds exotic, but its components are basic: regular root vegetables with a tangy-fruity peanut sauce. I realize this isn't close to a Joy of Cooking or Julia Child, but once you have the basics down, you'll want a book containing a variety of foods and flavors. The old classic Laurel's Kitchen has a great introduction, nutritional info., basic recipes, and a very homemade/homespun bent, even if it is decades old. Ditto the Vegetarian Epicure. Probably there isn't one bible but maybe a collection of 5 recipe books. Post Punk Kitchen is a great vegan resource: ppk.com. Also, Heidi Swanson's 101cookbooks.com. Many of these fit the bill you outline above re: some quick recipes, some slow, regular ingredients, weekday meals... Another excellent addition is the Candle Cafe Cookbook, which is vegan. I could live out of that thing year round. Mayonnaise only WISHES it could hold a candle to their vegan mayo recipe! It's that good.
I would like to recommend The Oh She Glows Cookbook. This book contains the low-calorie, processed food as well as nutrient-packed vegetables, fruits, nuts, whole grains recipes. If you are a vegan or you simply want to eat delicious food that just makes to be healthy, this cookbook is a must-have for anyone who wants to eat well.