Saturn SA-6 onboard film, 1964, view two. The launch vehicle is a Saturn-I; the vehicle's second stage is a S-IV. Video from 40390576 on YouTube.
In my time as an amateur spaceflight historian/shuttle pimper, I've found a lot of amazing channels while surfing around on YouTube. I've decided to occasionally profile some of the interesting things one can see while looking for space-y videos on YouTube.
This channel, called "40390576" (very enigmatic!), has an impressive catalog of vintage rocket/shuttle-related footage. There are a lot of great shots of rocket stage separations (such as the footage above of a S-IV second stage separating from the Saturn I launch vehicle). Also, if explosions are your thing, this channel has the market cornered on various rocket failures from the early days of the space program. This one from 1965 was particularly impressive, and I sincerely hope no one was injured in the resulting massive conflagration.
At any rate, this channel is regularly updated, and is an amazing find for any budding rocket engineers out there, or people who merely want to watch insane sh*t blow up. Check it out, whatever your viewing hungers are; you will not be disappointed.