Two suggestions that I recently (greatly) enjoyed in Paris:

Terminus Nord
Across the street from Gare du Nord. To me there is a romantic element to being across from the rail station and all the destinations that are therein possible. Okay, so I'm a romantic fool. Old school interior, white tablecloths, sparkling silver. Attentive, professional staff. I had the 'choucroute formidable'. And it was. I paid 33 euros.

La Comptoir de la Gastronomie
34, rue de Montmartre
This is a small restaurant that specializes in traditional, country-style dishes. The cassoulet is beyond excellent. Very affordable at 12 euros, but worth at least double that.
Attached to the restaurant is a small grocery selling a variety of specialty foods. This is currently my fave Parisian spot.

Enjoy!