From the Louvre can see the Arche de la Défense behind the Arc de Triomphe, you can go to these places by subway, which is very convenient and cheap (compared to Taxis, of course). And, then one day you cannot help to take a trip to the Palace of Versailles (try to arrive as early as you can, because in one day you won’t have time to tour the palace and gardens). Once, they nearly shut the gardens, but with me in them!...
Well this was a bit of my personal experience; I wish I was helpful...
Sincerely yours,
Your editor,
Charles McWerkillian