I will be in DC about a week and will be without my wife for two days during that time. She doesn't want to miss all the big stuff. What could I do with my son for two 8-hour days while my wife is in meetings?

He's 14, loves history and civil rights and of course rock music, guitars, iPhones., etc..

If you are interested in aircraft, the Udvar-Hazy Center near Washington Dulles is a great place to spend a day . . we were there for 8 hours and could have stayed longer

Perhaps make a list of the places you want to see and see if there are any in particular that she is not interested in. I know I am going to hear some back lash but I did not enjoy the Air and Space Museum. Don't know if it is because I lived through many of the changes in air travel and space programs but I found it a bit boring. You and your son many love it.

Other than that, everything is pretty exciting in DC.

Spy Museum?

I am never sure what people consider the "biggies." If your son is interested in history and the Civil Rights movement, the MLK memorial might make sense. The FDR memorial is also worth a visit.

The Newseum is quite interesting.
Maybe go to Old Town Alexandria or Mt. Vernon? There is also a National Historic site at Frederick Douglass's home, Cedar Hill. Georgetown has the C & O Canal National historic site

Couple more thoughts:

Smithsonian History and Technology
National Geographic Museum (Titanic exhibit starting later this month)
LIbrary of Congress
National Archives
Holocaust Memorial Museum
Arlington Cemetery

Given his interest, I would really suggest the national archives. They are more interesting than you'd think, and they have a good film as an introduction.

As far as the rock music, etc., I'd suggest the American History Museum. You would probably go there anyway, but they do have a musical instrument collection plus just all kinds of interesting things. Once they had a special exhibit of guitars, but all exhibits are temporal, of course.

YOu probably don't want to do this, but you could rent a car and go to Antietam in West Virginia (and Harpers Ferry if you had time) if he is really a Civil War buff. It is really fascinating, they have a good "museum" there, and good rangers who give the battlefield talk. Nearby is a small museum about medicine during the civil war. It's only a couple hours from Washington, although you may not want to do any traveling during your stay, but if you are here a whole week, then again, you might.
http://www.nps.gov/anti/supportyourpark/index.htm

Visit the White House? I don't even know if they still offer interior tours? I would love to do that.

Not off the eaten path, but maybe for the days your wife is with you:

From Fodor's Destinations:

White House

1600 Pennsylvania Avenue may be the best-known address in the United States. Every president but George Washington has lived here, and many heads of state have passed through its hallowed halls. The self-guided tour lets you follow their footsteps through the historic rooms. Note that it takes advance planning to visit the White House.

I meant "beaten" path!

Head over to Chinatown where you can visit Ford's Theater, The Portrait Gallery, The Spy Museum, and The National Museum of Crime and Punishment (those last two will cost you though).

A few months ago, we bought tickets through Groupon to an interactive game/walking tour called Stray Boots. It was a fun diversion from the usual treks through museums and monuments. We chose the Penn Quarter/Chinatown game. Fourteen is a good age for it.

http://www.strayboots.com/locations/...gton-dc/tours/

Stop to see Smokey Bear's desk in the Forest Service Information Center. It is the red brick building SE of the Washington Monument.
At the north end of the Ellipse you have a great view of the White House next to the Zero Milestone.

thanks

Not too far west of DC is Great Falls of the Potomac, a national park service place for a nice walk, look at the locks and falls, for a little"non city" activity.

If you get a nice day, you could also rent bicylces at Thompson Boat Center or Fletcher's Cove and ride them to Arlington Cemetary. There's a lot to see at Arlington, especially since your son likes history.

All good suggestions above - I would highlight:

1) American History

2) Nationall Archives

3) Newseum (if you decide to, go on the first day as it's a 2-day ticket).

4) The MLK Memorial if you want to spend some time walking outdoors.

One night during the week, a show at the Black Cat (one of the better rock venues in DC) might be an idea for him and one (or both) parents. They have an "all ages" policy (when the under 18 y.o. is accompanied by an adult...). Very close (a few blocks) to the U St. Metro station - an area also full of dining options.

http://www.blackcatdc.com/

You could let him loose in the Apple store in G'town for an hour or so while you explore the nearby neighborhood.

National Museum of the Marine Corp in Quantico, VA.

http://www.usmcmuseum.com/index.asp

We took our teen boys and they really enjoyed it. You could spend hours there.

I have to second going to the Newseum. We went there when our kids were 13 and 16 and they loved it. Lots of history, interactive exhibits, a 3D movie, they even have part of the Berlin Wall and a guard house there. Also, there is a museum underneath the Lincoln Memorial about the building of the memorial and important events that have been held there. We did not even discover this museum until we were on our second vacation to DC!

Taking off from what bardo said, it isnt tec-ee but getting out for a walk around the tidal basin tomsee the jefferson and roosevelt and (the new) martin luther king memorials is a great way to soak up a lot of american history. The korean war memorial is out that way, too.
You can go to the office of one (or both) of your senators and get tickets to the senate chambers. You can go to your congresspersons office snd get tickets to the congressional chambers. Call their offices first or look on line on their websites to see how each office does this. Esoecially if congress is in session, it is verry cool to see our govt at work. Sure a lot of folks go there, but it is still amazing.
While a lot of folks go to see the Declaration of independence and the Bill of Rights, i found the museum displays in the same building to be interesting and not crowded at all.
The National museum of the American Indian is very new with changing exhibits. Some may be right up your kid's alley if they are presented using a technology he is attracted to.
The many branches of the smithsonian are amazing and a peek at the website will reveal what cool stuff is available at all their locations, including temporary exhibits.
Good travels.

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I've been to DC 10 times, and didn't discover this until just now

The National museum of the American Indian is very new with changing exhibits.

And the cafe in the museum is really good (not inexpensive, though) -- all fresh "cuisines of the Americas and to explore the history of Native foods".