For recipe books, I second Ottolenghi's Plenty, I'd also suggest Cotter's Cafe Paradiso. Any Claudia Roden will also have loads of great veggie options.
I'm not veggie but do eat a lot of veggie food and have a few veggie friends , we usually go for Lebanese or Southern Indian. I could live on potato stuffed dosas with coconut relish.
Sree Krishna in Tooting or Bobby's in Leicester are places I used to love.
Years ago I was in a city, can't remember where, trying to book a meal for a large group with a vegetarian, I rang a number of restaurants, but could only find one which offered a veggie option. Starter was OK, when the mains came, we all got our mains on a large white hexagonal plate, with a small black hexagonal plate of 6 boiled/steamed vegetables arranged like a clock. Our Veggie got a large white hexagonal plate of vegetables as per our side plates..... plus a side plate of..........vegetables !!!
Even better was in Frankfurt, a colleague ordered a meal "without meat" and was given a plate of salad with a thick sauce on it, when she investigated, she found a pork fillet hidden underneath... they thought she just didn't want to see the meat, they couldn't comprehend "not wanting meat ".