Until recently, I recommended screenshooter for taking screenshots in flight simulator. However, not too long ago a friend turned me onto a new screenshooter utility for flight simulator that I can now not live without.
The change was especially important after I moved to dual wide screens. The old screenshooter still worked, but it wanted to shoot both monitors at once, typically leaving me with a screenshot that had to be edited and cropped to remove the half of it that I did not want (empty screen space).
Snapper.exe compensates for widescreen/dual monitors and does a great job at know which screen you are actually needing to screenshoot. It creates high quality images and allows you to configure where they will be saved. It will play a small audio cue when the screenshot has been taken which is especially important for knowing that you "really" took the shot when you wanted to.
It allows you to preview the shots within the utility, and also has some flight simulator specific features such as including latitude/longitude on the shot as well as information about altitude and location.
It is excellent. It is free, and it is tailor made for flight simulator users.
The website of the author is a bit sparse, but don't be fooled into thinking that the plain-jane website is an indication of the utility's worth. Take a look at it. I have been using it for 2 years...and can not live without it now.
It can be found Here. (Snapper.exe Author Website)