I can't recommend 
Hotel Montpensier enough.  At < €100/night (as low as < €70 for a single bed room) and 
across the street from the Louvre, it couldn't be beat for us.  If scenic views and lavish interiors are what you're looking for in a hotel, not so much.  But it's clean, the staff is friendly, and it's 
across the street from the Louvre.