We are both vegan, so no howls of laughter here! Although it is indeed funny that the first answer whenever this is asked is falafel in the Marais! So, another vote for falafel in the Marais, for us Mi-Va-Mi. If you are willing to "sin" and consume a bit of dairy, the nearby Florence Kahn Bakery has excellent desserts.
Hank also has a vegan pizza restaurant, which is part of the same website as his burger place. I despise cheese so I didn't try any, but Denis was pleased with his selection of take-out slices.
We are fond of south Indian restaurants, of which there are several in Paris. I didn't write it down, but we both think it was Saravanaa Bhavan.
Although we never had good timing, there seemed to be some vegan tagines at lunch time in a shop at Marche des Enfants Rouges.
We always get a kitchen and love shopping at farmers markets. Both Marche Popincourt (Tuesday and Friday mornings) and Marche Bastille (Wednesday and Sunday mornings) have vendors with prepared food options that are vegan. We bought lots of hummus and pita bread. Throw in some salads and you're set. And the fresh fruits are lovely, yum, the strawberries when we were there. Oh, and the cherries.
After a delightful experience at a Vietnamese restaurant in Berlin, I'd like to look for something similar in Paris. Just haven't gotten around to that research yet.
A friend of our recommended Le Potager du Marais, so we'll be trying that this time around.
I'm not sure if some of the Naturalia locations have prepared foods or not. I know we got nice breads for peanut butter and jelly sandwiches from them.
As Pam said, don't forget to check Happy Cow.
@ Pam: So are the sorbetti at Amorino locations as good as in Italy? There seems to be one quite close to our apartment.........