Romantic? Dinner at the restaurant on the island in the Lac Inferieur at Bois de Boulogne, weather obviously permitting. Can't recall the name, but it's the only one there. Neither cheap nor expensive and the food is very nice but not exquisite, but the ambiance on a Summer evening is to die for.

I agree being in Paris is romantic! Good walking distance information and websites.
What about the dinner river cruises are they worthwhile?

Be careful with your wine in Luxembourg Gardens. It's not legal but usually you can get away with it if you're careful.