F-15 ACTIVE
Developed as a technology demonstrator, the F-15 STOL/MTD carried out research for studying the effects of thrust vectoring and enhanced maneuverability.
F-22 Raptor
As a product of the United States Air Force's Advanced Tactical Fighter (ATF) program, the aircraft was designed as an air superiority fighter, but also incorporates ground attack, electronic warfare, and signals intelligence capabilities.
Su-37 Terminator
The Sukhoi Su-37 was a single-seat twin-engine aircraft designed by the Sukhoi Design Bureau which served as a technology demonstrator. It met the need to enhance pilot control of the Su-27M (later renamed Su-35), a further development of the Su-27.
SR-71 Blackbird
The Lockheed SR-71 "Blackbird" is a retired long-range, high-altitude, Mach 3+ strategic reconnaissance aircraft developed and manufactured by the American aerospace company Lockheed Corporation. During missions, the SR-71 operated at high speeds and altitudes (Mach 3.2 and 85,000 ft; 26,000 m), allowing it to evade or outrace threats. If a surface-to-air missile launch was detected, the standard evasive action was to accelerate and outpace the missile.
MiG-25 Foxbat
The first prototype flew in 1964 and the aircraft entered service in 1970. Although it was capable of reaching Mach 3.2+, this would result in the engines accelerating out of control and needing replacement, therefore the operational top speed was limited to Mach 2.83. The MiG-25 features a powerful radar and four air-to-air missiles, and it still has the world record for reached altitude of 38 km (125,000 ft).
What I like about them
Few things are as interesting as machines that allow man to fly.
The fact that human ingenuity allows for something as absurd as searing through the heavens as a bird would, is just incomparable to anything else for me.
Particularly intriguing are military aircraft; as they're built for military purposes, programs intended to make them receive insanely high budgets, and so engineers can really go all out on the technology.
All of them are interesting in different ways, but a few of them stand out for me; above this text you can see a slideshow with their pictures.