Ah, the SR-71 Blackbird. Everything an Incredibly Cool Jet should look like (i.e., bearing a tremendous resemblance to stuff I drew on scrap paper as a kid).
Rare photos of the SR-71 Blackbird show its amazing history
The SR-71 Blackbird is, without a doubt, the most advanced airplane ever built in relation to the technology available at the time. It broke all aviation records, it flew incredible missions, and it became the stuff of legend. Lockheed Martin published its history in this collection of high resolution scans of old photos.
Second prettiest. My vote goes to the ME-262.
+William Altman The Me262 certainly ranks up there, but I still have to give the nod to the Blackbird.