Good to see Gobo mentioned adamak ...I'm going to go there for the first time next week.

Some of my favorites and not so favs:

New York:

Pure Food and Wine - wonderful raw food - vegan, I believe (I so love raw, vegan cheeses)
Artisanal - not a vegetarian restaurant, but many good veg dishes
Chicago:

Tru's vegetarian tasting menu - a little more creative than
Charlie Trotter's vegetarian tasting menu but both excellent
Green Zebra

San Francisco:
Greens - good for more basic fare whereas the
all-vegan Millennium usually has some surprises on the menu
Fleur de Lys has a vegetarian tasting menu, but I didn't find it very inspired last I was there
Michael Mina also has a veg tasting menu
French Laundry in Yountville veg menu that's OK but not great

Las Vegas:

Cafe Ba Ba Reeba dmfriedman picked this and while it's certainly not all veg, they have some really good veg small plates. I stop there for lunch always now when I'm in Vegas.

Paris:

Pierre Gagnaire does a wonderful feast for vegetarians that is not on the menu. it's about 12 courses.

I'll add many more soon ...