Going to give props to the outfit through which we rented our apartment at 41 Quai de Bourbon, on the 6th floor: www.parisaddress.com. There are a number of sites that offer short term apartment rentals. Parisaddress's site is by far the best, and their prices are pretty good, though in one case that we saw, the same apartment was listed on another site and was cheaper. I was asked, how do you trust these guys? After all, you're sending them a lot of money. It's true that it was blind trust, but everything was fine. The payment can be made online (the deposit is mandatory online, but you have the option of paying in person on arrival). One thing to note is that you might need to clear your US credit card with your issuer before attempting the online payment -- I had to do this; it was declined otherwise. The payment is via Societe General, a major French bank, so in terms of security, that seems fine. Their communication was prompt and professional, and they were pro-active...
Stuff that I've seen, done or used