That huge road that runs up to the Arc Du Triumph (I think it's there, and yeah I probably spelt it wrong) would be cool, you could get some awesome long exposures there as it's always stupidly busy with cars.
Oh and remember that you can't use (i.e. sell or distribute) photos of the Eiffel Tower at night commercially without permission (doubt you were gonna do that anyway but it's usefull info anyway).