Inside the Louvre pyramid lobby. There are three wings, Richelieu, Sully and the one most tourists head for immediately is Denon, where the Mona Lisa resides.
To avoid lining up for ages for almost all Paris attractions but especially the Louvre Museum, tourists need to do two things: a) buy a Museum Pass online, at a tourist office or some other museum that has shorter lines (such as Ste-Chapelle, nearby) b) arrive as close as possible to opening time at 9am (closed Tuesdays). See Louvre guide.
Denon wing first hall.
The Mona Lisa scrum. It is possible to get to the front and contemplate the smile, but requires patience and fortitude.
The Venus de Milo. Fortunately the Louvre is so huge that few exhibits see massive crowds.