When I test drove the Model S a few weeks ago I paid no attention to the floor mats. But based on my experience with many other cars, this seems to be one area where things tend to be done on the cheap. I've frequently bought Lloyd's mats to replace the OEM mats. I hope this won't be necessary on the Model S, but just in case I emailed Lloyd's today to inquire if they plan to make Model S mats. No reply as yet.
Here's a link to the Lloyd's web page on their top-of-the-line Luxe mats, which I've found to be of extraordinary quality.
Luxe Mats | Lloyd Mats