There's been a heck of a lot of good aviation movies, a few great ones (most of which are already mentioned in this thread), and a few duds (also mentioned in this thread). But there are two that I find myself watching again and again:

The Great Waldo Pepper - already mentioned several times in this thread. There's just something about this flick that brings me back to it time and time again.

Deadly Encounter - Stars Larry Hagman, Susan Anspach, and James Gammon. There is some absolutely amazing, over-the-top helicopter flying in this one. Rotorheads need to see it!!