The thing with wings

Dragon wings tend to be more or less bat-based, but photos of bats in flight tend to be rarer than ones of birds in flight, making studies a bit more difficult.

For birds I recommend the deviantart account of Cheryl Moore, where you can find a great number of photos of birds in flight - most of them white birds, meaning there is no pattern on the feathers distracting from the shape.

As for bats, during the last week some photos of bats drinking from a pond in flight went through the bits of blogosphere I watch. Looking up Kim Taylor brought up Warren Photographic, which has more (albeit smaller) photos of bats in flight.

On Deviantart I found one compact tutorial on bat wings by cactusart.

The wing tutorial by Kandice Zimbleman-Wang may be a bit weird on the formatting and spelling side, but content-wise I find it very helpful.

For the sake of completeness and comparison, you could look at pterosaurs wings, too. (What intersts me more after a bit of poking around wikipedia are the various head shapes, though. Fascinating.)