Lockheed Martin's Skunk Works says the replacement it's proposing for the SR-71 spy plane, the SR-72, is a Mach 6 drone that doesn't need to be stealthy because it's so fast.
http://www.avweb.com/avwebflash/news...2220910-1.html
It's been a long long time for something to out perform the SR-71, great stuff.