Have seen some of these fly back when I was a kid. Convair (later General Dynamics) used to have an airshow in Fort Worth all the time and we would go because my parents worked out there. My dad actually worked on these. I always thought it looked like it was going a million miles an hour even when it was sitting still.
I also saw the XB-70 fly at one of those shows. I think they may still have one of those at the museum at Wright-Patterson in Dayton. We lived there for a few years, too.
I've walked underneath that XB-70 at WP AFB in Dayton. It was a religious experience of sorts.
Only two functional XB-70s were built. One crashed during testing in California (chase plane clipped it, causing it to go down), so the one in Dayton is the only one left.
http://en.wikipedia.org/wiki/North_American_XB-70_ValkyrieWhile I think some of the new aircraft are cool (read: F-22), I just don't think that Aviation design is quite as exciting as it was back in the 50s and 60s. A lot of the cool stuff comes from that era...