No, it's not World War 2 again... it's a massive flyover of vintage WW2 bombers and fighter.
If you're downtown near the National Mall or along the flightpath, go out around noon to see the "Arsenal of Democracy Flyover" dominate the DC skyline. (They should be over the Lincoln Memorial by 12:10pm, headed over the Mall and then left after the Capitol.)
You can check out the list of formations that you will see coming in over the city. And here is the official Arsenal of Democracy Flyover Fact Sheet (pdf).
And here's a cool Plane-Spotting Guide to help you identify the planes (over 70 are scheduled to participate). Considering these are all prop-planes, it should be LOUD and glorious.
Update -- now with far away pix!