As for the whole question of whether Pink Floyd did this on purpose, there is simply no way they could have. Kenata points out in his DSOTM w/u that the music for the album had been completed at least a year before it was released, putting the writing of the music around 1971. The technology necessary for the band to synch up their music to an already existing piece of film and not have anyone find out simply did not exist back then. They would have needed to get their hands on an actual film print of the movie and then rent out the necessary film and sound editing facilities in order to make the synch. I doubt that facilities like this existed outside of a major motion picture scoring studio at the time. The fact that the synch holds up over the second and even third repeats should prove that it is unintentional, as it would be impossible to set up something like that on purpose with the technology at the time.
While Dark Side of the Rainbow is certainly the most famous Pink Floyd synch, there are many others that can be found online. I cannot testify to the validity of these, but this really seems like an “eye of the beholder” thing no matter what. I can say that I have done Dark Side of the Rainbow and found it to be very, very cool.
All of these assume that you have the album paused and ready to go.
These are just the synchs that I have been able to find related to Pink Floyd, there are many others that can be found featuring other bands and other movies (Fantasia - Siamese Dream and Stir of Echoes - Led Zeppelin IV for example).
After a very interesting experience with The Wizard of Oz, I tried a few of the other combos I found online, mostly featuring movies and albums I already had access to. I have been very disappointed thus far. So I’m going to say when trying any of these that you might come across, use of hallucinogenic drugs is recommended. :-)