If money is no object, how about a trip on the Orient Express? It has managed to build its name up over the years to be synonamous with romance and luxury travel.
Leaves from various "romantic" cities in Europe for overnight trips and definitely do-able for a weekend. http://www.orient-express.com/web/vsoe/journeys.jsp
If you decide to do just Paris, there's nothing like the Four Seasons George V: http://www.fourseasons.com/paris/