Great Thai Cookbooks: easily adaptable to meatless?
For solid, simple and rather basic recipes, I like Nancie McDermott's Real Vegetarian Thai. To my tastes, the spice level are a bit mild in this book, but it lays out a good range of dishes that lend themselves well to tweaking. More complex and authentic recipes are in the great Thai Vegetarian Cooking by Vatcharin Bhumichitr. It's out of print, but you can still find used copies on Amazon, Bookfinder.com and eBay.
David Thompson's would probably be the authoritative one if you want really authentic (and challenging) recipes. It uses fish-derived ingredients a lot, but given those constraints, there should be some meatless options.
I have Chat Mingkwan's book "Buddha's Table". I think it's at least Ok, given that there aren't many vegetarian Thai cookbooks out there.