Even though they serve meat, Le Pain is one of my all time favourite restaurants not just in Paris. They manage to keep their standard high, the quality of the food is really good and then they have everything clearly labeled 'vegan' (I wish all restaurants would do that!) Their restaurants are ALWAYS busy, but the interior is nice and the atmosphere is relaxed and friendly. Their botanic brunch is a fairly reasonable deal. Also the take-away option is much cheaper. They should label the food on the counter though.. in case someone like me does not know it by heart!
I don't even mind the fact that they are not vegetarian as that way I can go with my non-veg friends and they can accidentally taste the amazing cruelty-free food!