My preference is the XB-70 Valkyrie[0], one of the only other manned aircraft comparable to the SR-71 in my eyes. The droop nose, the incredible dropping wing tips, six engines… To me, the Valkyrie looks like the kind of plane you'd see in a Gundam anime series.
Shout out also to the MiG-25 Foxbat[1]. While not a particularly beautiful aircraft, it's made of steel and could go Mach 3.2 if they didn't want to use it again.
[0] https://en.wikipedia.org/wiki/North_American_XB-70_Valkyrie