Eiffel Tower Tickets Pre-booking

The good news is that you can book entry times at the Eiffel Tower online, saving long waiting times on entry lines.
The bad news is that there are websites that will sell you tickets at a healthy, and unnecessary, mark up.  Purchase your tickets directly from Eiffel Tower site http://toureiffel.com/.  Visiting the tower a little before or around sunset is a lovely time to go to watch the lights and illuminations of the major monuments coming on.