Here are some photos from the "Research and Development" Gallery at the US Air Force Museum, Wright-Patterson Air Force Base, Dayton OH.
P-59 Airacomet prototype. first American jet fighter.
XF-85 Goblin
Avrocar
XH-26 Jet Jeep
YF-12, experimental high-speed interceptor based on the SR-71 spy plane
P-75 Eagle, an experimental fighter with jet engines and two counter-rotating propellers
F-107, an experimental fighter
Ryan X-13 Vertijet. An early experiment in short-takeoff.
Hawker Kestrel, an early version of the Harrier jump jet
Tacit Blue, an experimental stealth airplane
YF-23 Black Widow II, a stealth fighter. It lost out to the F-22 Raptor and was never produced