Vegetable Garden is decent, but there is a better (IMHO) vegetarian Chinese place in Rockville, called Yuan Fu Vegetarian. It's on Rockville Pike just south of downtown Rockville - look for a small strip mall with an Enterprise car rental, liquor store, and dry cleaners. There's a big green sign which just says "VEGETARIAN".

If you like Indian food, there are 2 good all-veg Indian places in Takoma Park, at the intersection of New Hampshire & University. I prefer Udupi Palace but apparently Woodlands also has its followers.

Also, there's a Kosher pizza place in Wheaton called the Nut House which has some vegetarian toppings ("sausage", "pepperoni", etc.). The pizza is decent. Unfortunately the hours are somewhat inconvenient (it closes at about 9 PM, I think, and is of course closed Friday night and all day Saturday).