One of my favorite things to do in Paris is bicycle through the city.
The city has a network of automated bicycle rental stations and the cost is very reasonable...check out the website:
Vélib' - vélos en libre-service à Paris - Site Officiel - Paris
There is an english language pamphlet you can download from the site. You'll need to have one of those "smart" credit cards with the embedded chip and PIN in order to use the system. Its an absolute blast to pedal around the streets of Paris.