http://www.criticalpast.com/
I've spent the last 45 minutes surfing through this thing. Loads of archival film footage and news reel clips, some with sound, some without. If you do a search for whatever US aircraft you're interested in, you'll probably find something. Lots of WWII footage, not just airplanes. They've also got a good selection from Korea and Vietnam.
Ben
Wow. Thanks Ben. Some nice 105 footage from Goldsboro if you do a 105 search!