The Park Hyatt is quite nice but not really in the Dupont neighborhood (though it is walkable to it - about 6 blocks).

Do you really need to stay near National Airport? The airport is less than a 15 minute taxi from downtown.

Only staying there as I can drop off the family at the hotel, and then take the rental car to make business visits. Most of the hotels in DC cost an arm and a leg to park the car.

River Inn is really nice. The location isn't as good as Dupont Circle in terms of nightlife, but I love the actual hotel and there are some good places to eat around. 2000 Penn is close by, which houses Kinkeads (best seafood in DC IMHO) and Bertuccis. Plus the Watergate Safeway is less than a 10 minute walk away.