The F-15 Eagle (in this case the "slam" variant, which is uber cool) is quite simply the most beautiful Milcraft ever created. I love the clean profiles of the F-16 Falcon and the F-18 (Super) Hornet, and of course there will never be a more perfect craft using our current knowledge of physics than the SR-71 Blackbird.
The F-22 Raptor (and its predecessor the F-21 Lightning) and the poor doomed to failure F-35 JSF are cool, but not beautiful.
For elegance in the sky, the F-15 will never be bested: