City Segway Tours offers guided English-speaking Segway tours 3 times a day.  They use the latest Segways (the i2) and see all the major sites (Eiffel Tower, Louvre, Champs-Elysees Napoleon's Tomb, Les Invalides...) in the city.  Reservations are required and can be made via their website or by calling their office (01.56.58.10.54).  Groups are a maximum of 8 people and there is a minimum age of 12 years old.  The guides are all native English speaking and seemed to have great knowledge of the city and were quite personable.