The first Sunday of every month is Museum day in Paris. That means you get to go into any Museum for free! I was at the Louvre on the first Museum day of 2010. Only problem is that you (by that I mean I) can probably only last about half a day with endless paintings of long long ago. They are beautiful but a little too tiring to go on and on.
Pack some sandwichs, chocolate bars and beverages, the queue for food in the Louvre can get quite long. Find a quiet corner (there is a seating area near the cloakroom, it's a nice spot to eat without too many people walking around you) to take a break when you are done viewing the endless paintings.
The other museum that I highly recommend is Museum D'orsay. It's along Line C at station Musee D'Orsay.
That night we went to the Eiffel Tower. How much do Souvenirs really cost?
Saving tip: If you can't see all the Museums in Paris on the free Sunday and cannot afford to stay a month. There's a ticket for "students" or a younger age group sometimes below 24 or below 26. Ask when in doubt.
Note: I don't think the french guy behind the counter can really tell what age Asians are, and we can look really young to them because of the relative build. And who goes sightseeing with his/her passport or student ID or any ID for that matter anyway. ;)
