I figured since I submitted a song, I would post why I submitted it for listening.
When people ask "what is a good instrumental rock song" most people will point to YYZ, by Rush, from the Moving Pictures album. And yes, that is a great instrumental song. But then you introduce yourself to Pink Floyd, and realize they are the kings of instrumental songs.
So that brings us to "One Of These Days", the opening track from the Meddle album. It starts quiet, but then the DOUBLE bass line kicks in. It's almost like a duel between Roger Waters and David Gilmour. At about 2:07 the drums make their first appearance. 2:49 the bass goes away, and the song transfers into what people call "Doctor Who mode", as it sounds like Pink Floyd's own version of the Doctor Who theme (especially when they play it live). At 3:30 the drums kick back in, and at 3:37, drummer Nick Mason (behind walls and walls of distortion) says the title of the track, and then the song EXPLODES into a race of sounds for the duration of the song and never lets you go.
That's why this is the greatest rock instrumental of all time. That's why I submitted it for listening.