Some welcome news if you plan a visit the Eiffel Tower and also would like to avoid hour long waits in lines. A new reservation system has been introduced on their website, where you can reserve and prepay tickets for specific timeperiods of the day.^

You seem to be able to make reservations about a week ahead and choose between tickets to the second floor level or all the way to the top.

http://www.tour-eiffel.fr/teiffel/uk/index.html