There’s a 40 minute version of The Orb’s Blue Room.
Actually, many CDs feel like one long album-length song to me.
But anyway, one of the longest “songs” I know is “A Long Day” by the Polyphonic Spree. 36:30 (I think) of meaningless humming without any rhythm or melody at all. I have no idea what its purpose is, actually.
Speaking of things without rhythm or melody, I really like “Revolution 9” from the beatles, which runs 7:something. Not ridiculously long, but it feels pretty long.
It’s a great pick.
Bye Bye Miss American Pie a bit over 11 minutes I think.
In the '60s there was a very long piece, more spoken than sung. A rather hypnotic story…The guy did Levi’s® commercials later. Anyone remember this? I didn’t drop that much. 
Both reasons I came to this thread. Thanks for getting to them before me. 
Also; almost anything by Ash Ra Temple.
And the Microphones’ “the sun.”
It runs about 8:30.
VU - “Some Kind Of Love (live)” 10:21
Lou Reed - “Street Hassle” 10:53
Led Zeppelin - “Achilles Last Stand” - 10:22
Miles Davis - “All Blues” 11:53
And those are just what I have here at work on the iTunes.
I love playing the long stuff in the office, just to see if anybody notices:
By time from my iTunes:
Djed by Tortoise 20:57 - theres also an UNKLE remix thats about 9 minutes
Summer Eyes by The Young Gods 19:55
3 Days by Janes Addiction 10:48
Babe, i’m on fire by Nick Cave & his bag of Seeds 14:46
Didn’t we deserve a look at you the way you really are by Shellac 12:19
the last two get special mention because its the same hammering riff over and over again. RAWK!
Also special props to Explosions in the Sky, who kick Mogwais arse, most of their tunes are around the 10 minute mark
And: KASHMIR - the orchestra version off Page & Plant unplugged - the version of Dazed and Confused from Song remains the Same is about 26 minutes too.
There was also “Legend of the USS Titanic” by Jamie Brockett. I don’t know the timing (All-Music doesn’t have the information), but it took up the entire side of an album. It got a lot of FM airplay.
“Hush Hush” by The Siegel-Schwall Band. One of the most infectious numbers ever performs – you can’t help tapping your feet to it.
King Crimson did many long songs. “Twenty-First Century Schizoid Man” is over 7 minutes, and “In the Court of the Crimson King” is over nine. There are others.
Macdonald and Giles (who started with King Crimson) did “Suite in C” and “Birdman.”
Rick Wakeman did some 6+ minute songs on “The Six Wives of Henry VIII,” but his “Journey to the Center of the Earth” was just one composition that covered an entire album.
British progressive/art rock of the early 70s often had long songs; it’s a shame it went out of style. The genre was far from played out.
are you thinking of Atlantis by Donovan, by any chance?
… and i can’t believe we’ve gotten this far without anyone mentioning Stairway to Heaven by Led Zeppelin. clocks in a bit over 8 minutes, IIRC.
I believe “Epitaph” is quite long, as well. Excellent track.
Dammit, ultrafilter! You stole both my answers from me!
I was also going to mention Black Rose Immortal by Opeth and Light of Day, Day of Darkness by Green Carnation. The latter is the greatest road trip song ever.
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I just read the title of this thread as “Best Love Songs” and was racking my brain trying to figure out when I posted in that thread.
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Some of these don’t compete (lengthwise) with the 15+ minute jams mentioned so far, but still exceed the typical pop/rock song in scope and quality.
David Bowie - Width of a Circle (a mere 8:05)
Suede - The Asphalt World (9:25)
Nick Cave - Babe, I’m on Fire (14:25)
Prince - Purple Rain (8:25)
Sigur Rós - Svefn-G-Englar (10:04)
Sigur Rós - Viõrar Vel Til Loftárasa (10:17)
Oasis - Champange Supernova (7:28)
The Chemical Brothers - The Private Psychedelic Reel (9:28)
Underworld - MMM Skyscraper I Love You (13:08)
Rush - Xanadu
Jon & Vangelis - The Friends of Mr. Cairo
Yes - And You and I
Supertramp - Fool’s Overture
ELP - Tarkus
Led Zeppelin - In the Light
What exactly is he speaking to (with regards to this thread)? 
Uneasy Rider by Charlie Daniels.
Depends on whether you consider Earth’s Earth 2 as one song or not.
From my iTunes library:
Black Sabbath - “Wicked World” off of Past Lives - 18:55
Metallica - From Live Sht: Binge and Purge*: “Seek and Destroy” - 18:08; From S&M: “Outlaw Torn” - 9:58; From Garage Inc: “Mercyful Fate” - 11:11
Lynyrd Skynyrd - “Free Bird” - Live version
Creedence Clearwater Revival - “I Heard it Through the Grapevine” - 11:06
Tool - “Reflection” - 11:07 and “Lateralus” - 9:24