A little over two hours into my flight back home from attending GIG I noticed a light flash on the left wing. I assumed it was a light beacon on the aircraft. But when I saw the flash again I looked past the left wingtip and saw a large thunderstorm with lightning flashing within. I took a few cell phone pictures but wasn't happy with any of them. So I dug my Nikon out of its bag, attached the 50mm lens on it, and snapped a few more pictures as the storm moved past the wingtip.
This was total luck. I took a guess when another bolt of lightning might appear. It's a long hand-held exposure (around 1/2 second ) so when the picture is viewed at 100% the bolt is smeared (the orange blur at the bottom-left of the second picture is of a passenger behind me reading a book). But considering I'd never gotten a really good picture of lightning before, this will work for me.
(Shot with the Nikon D300 using the 50mm lens; aperture-priority, with aperture set to f/2.8; camera chose shutter speed of 1/2 second (top) and 0.7 second (bottom) at ISO 1000; spot-metered; auto white balance; normal JPG.)