I'll be going to DC with my wife in late Dec and would like to take her out for a romantic dinner. We'll be staying in Arlington but plan on spending the days in town sightseeing.

Thanks in advance.

The perennial favorites, all very pricey:

L'Auberge Chez François, Great Falls.

Inn at Little Washington, Washington, Virginia. Booking this late may be a problem though and it's a hike from Arlington.

1789, Georgetown. Perhaps your best bet.

Here's another vote for L'Auberge Chez François in Great Falls. It's a coat & tie place, and reservations a must. Here's a link to their web site:
http://www.aubergefrancois.com/

Village Bistro in Arlington is one of my favorites. It is in a strip of restaurants on Wilson Blvd, between Courthouse and Rosslyn.

Great Falls and Little Washington are a little distance but those restaurants are great. Another really good french restaurant is Gerard's Place on 15th St NW - the food is superb and it's pricey.