I completely forgot about the Jacquemart-Andre museum on the right bank - it's a small, private museum (so not covered by the museum pass) housed in a gorgeous mansion - and the exhibits are right there - no ropes - so you can get (respectfully) nose-to-nose with Rembrandts.

Definitely spend some time on the Ile St-Louis. At the Notre Dame end you should order some hot chocolate at Cafe Flore en l'Ile - they bring it to you French style - a little jug of melted chocolate and a jug of steaming, frothed milk - mix and enjoy (it's heavenly.) It's a little touristy, but I had a LOT of fun at Nos Ancetres les Galois - it's not like you'd expect a Parisian restaurant to be. Caveat: watch out for the wine that you get from the barrel up front (you get an empty earthenware jug and directions to the barrel) - that stuff sneaks up on you.

Under no circumstances would I recommend driving in Paris. Those guys make Boston drivers look courteous. There's nowhere to park, anyway...