On the first Sunday of every month the national galleries in France are free. On subsequent Sundays it's half-price. Judging by the line in front of the Musée d'Orsay and the crowd inside the Louvre today, this fact is no secret in Paris. Nonetheless, if you're looking for a cheap way to see some wonderful art and can deal with the crowds, it might be worth it. We skipped the Louvre Top 10 (Mona Lisa, Venus de Milo, etc.) and went to see the objets d'art from Napoleon III's Apartments, The Restoration, and the July Monarchy.
And because we know a "secret" entrance to the Louvre, there was no waiting in line! Of course, I can't tell you where this secret entrance is because if I do, it won't be a secret much longer and then it will have long lines just like the main pyramid entrance. If you're planning a trip to Paris soon and want to know (and will keep it a secret), email me and I'll tell you where it is.