I was born the same year this photo was taken of the #3 North American X-15 sitting on a dry lakebed, and I gotta say it was pretty cool growing up with the X-15 program still operational. This image seems to say it all when it comes to how cool the X-15 is. It's lean, mean and so secure in what it's designed to do that it didn't even need wheels on the main gear! It's part Batman and part astronaut all rolled into one.
This is the #3 aircraft (the last one built) - and tragically, it's the only one totally lost in the program. On November 15, 1967 Michael James Adams lost his life when the X-15 went out of control and broke apart. Accident details from his wiki entry: Adams' seventh X-15 flight, flight 3-65-97, took place on 15 November 1967. He reached a peak altitude of 266,000 feet (81 km); the nose of the aircraft was off heading by 15 degrees to the right. While descending, at 230,000 feet (70 km) the aircraft encountered rapidly increasing aerodynamic pressure which impinged on the airframe, causing the X-15 to enter a violent Mach 5 spin. As the X-15 neared 65,000 feet, it was diving at Mach 3.93 and experiencing more than 15-g vertically (positive and negative), and 8-g laterally, which inevitably exceeded the design limits of the aircraft. The aircraft broke up 10 minutes and 35 seconds after launch, killing Adams. The United States Air Force posthumously awarded him astronaut Wings for his last flight.
The other two X-15's remain today with #1 at the National Air & Space Museum and #2 at the Air Force Museum. The X-15 represents brave men courageously exploring the boundary of earth... and the risks that came with it.