You must try the Chha Kroeng (with tofu), which is stir-fry of tofu, onions, green bell peppers, in a strong gingery/garlicy/curry sauce with crushed peanuts. Yum!
For the (overly) picky, it's worth noting that if you order vegetarian spring rolls, they're probably taking pre-made spring rolls with shrimp, pulling the shrimp out, and serving it to you. This doesn't bother me much, except when a little piece of shrimp shell is left in. But if this is something that would freak you out, skip the spring rolls.
If you order a young coconut to drink, you get a coconut with one end hacked off, along with a straw to drink the juice, and a spoon to scrape out the soft insides. This is quite a treat if you've never had coconut juice before. It is not at all like the coconut flavors found in things like western-style cakes or candy bars, as it's much lighter and less sweet.
They also have some vegan desserts, including one made from sticky rice, coconut milk and dried fruit.