Depending on where you are some of my favorites within 30-45 mins of the city are:
Westfields - west in VA
Lake Presidential - east in MD (probably my favorite in the area so far)
Blue Mash and Worthington Manor - north in MD
I haven't played Laurel Hill yet, but it's supposedly one of the best in all of VA.
Another option would be East Potomac in the city. They have a full 18, a 9 hole exec, and a par 3 course. The courses are nothing spectacular by any means but the location is tough to beat - on the Potomac with views of the monuments from just about every shot. It doesn't hurt that it's cheap (by DC standards) as well.
As for sabram's suggestions, I haven't played Stonewall but hear nothing but good things about it. However, I'd be careful about Augustine. I played it twice this past summer and the conditions were brutal. It's a shame because the layout is good and though I'd never played it before this year, I've heard it was considered one of the best in the area a few years ago.