Among plenty of vegetarian restaurants in Manhattan, here are my fav -
Gobo
http://www.goborestaurant.com/
Owned by the sons of Zen Palate founder. Food is similiar to ZP, but hipper and younger. Plus they serve alcohol.
Candle 79
http://www.candlecafe.com/
They own both the upscaled Candle 79 on UES, and the casual restaurant Candle Cafe. I prefer 79 more. Good romantic place for dates.
Vegetarian Dim Sum House
http://www.vegetariandshouse.com/
In Chinatown. Lots of mock meat dishes, very authentic. I can go vegan forever if I can eat their dishes everyday. Plus $5 get you enough food for lunch and dinner.
Vegetarian Paradise 2
http://www.vp2-nyc.com/
Cheap and tasty.
Natural Gourmet Institute
http://www.naturalgourmetschool.com/...-dinner-c.html
This one I haven't tried yet. Similiar to CIA, they have veggie cooking class and Friday night dinner.
Some of the veggie places I found overrated -
Hangawi (Korean) - small dish, tasteless, not authentic, more fluff than stuff. Go try any other Korean restaurants on that street and you'll have better meals.
Devi (Indian) - Again, you can get much better Indian food anywhere else in town. Not sure why this place gets rave review. I found the food so-so (esp veggie dish), poor services and overpriced.
Spring Street Natural Restaurant (American) - I like the diner concept. Food was alright. Slightly overpriced.