The New York Times has done a detailed and informed piece on how to experience the best of Paris on a budget, which is worth a read. I would add dinner at Chez Janou, an unpretentious but delicious restaurant with a provencale menu, courteous staff and color. It's steps from my favorite square in Paris, Place des Vosges. Also, what is a day in a heavenly city without the best ice cream on the planet? Bertillon, a delectable shop on the Ile Saint Louis in the heart of the city, wins as the best place to soothe a sweet tooth I have ever been.