Paris for a week, Le Marais and my birthday!
Depends on what you're willing spend. For a fun, moderately priced bistro, le Taxi Jaune on the rue Chapon in the 3rd... 30 to 40€. For an upmarket birthday, la Grande Cascade in the Bois de Boulogne... 100€ for lunch.
Whatever you do, try to weave in a visit to the Piano Bar at the Closerie des Lilas on the boulevard Montparnasse.