The Commemorative Air Force has a Summer Tour where you can fly in one:



I've volunteered many times to work as ground crew for Maid in the Shade and it is a blast. On one ride, I got to buzz my house with my kids in the backyard at about 1000 feet.

You can also fly in a B-17 on the tour. I've flown in both, and it is pretty terrifying to be in an un-pressurized plane. Makes you really appreciate the sacrifices that were made by those who flew those amazing machines.