I’ve always liked long songs, so I’m looking for some suggestions.
My nomination?
Jethro Tull - Thick as a Brick, parts 1 and 2, adding up to a whopping 43:28! Even with that excessive length, I’m always disappointed when the song ends and end up wishing it was even longer.
Jenny Ondioline by Stereolab is an amazing song that runs about 18 minutes.
Pink Floyd is the champion, with “Astronomy Domine,” "Careful With that Axe, Eugene, “Set the Controls for the Heart of the Sun,” “Atom Heart Mother,” “Echoes,” and “Shine on You Crazy Diamond.” Their best works were all over eight minutes.
King Crimson, “The Court of the Crimson King” (“21st Century Schizoid Man” is 40 seconds short, alas).
Soft Machine, “Moon in June” (though anything on their album “Third” qualifies).
Allman Brothers, “Whipping Post” (live version), “Mountain Jam,” and “In Memory of Elizabeth Reed.”
Frank Zappa, “Willie the Pimp”
I’ll throw out a whole bunch of nominations:
I second the live versions of “Whipping Post” and “Elizabeth Reed”
“Voodo Child” by Jimi Hendrix on Electric Ladyland. Hendrix on guitar, Jack Cassidy on bass, Steve Winwood on organ, and Noel Redding on drums. Rock ‘n’ roll never got any better than this.
“Machine Gun” (Band of Gypsys version) by Jimmy Hendrix. Actually the Isle of Wight version is better, but it’s only 7:35 in length.
HELL, anything Hendrix and the Allman Brothers ever did that’s over eight minutes in length is worth listening to.
“Heard It Through the Grapevine” by CCR
“Beginnings” by Chicago. The full-length version is very close to 8 minutes, I believe, and it’s a great song.
“Morning Dew” by the Grateful Dead on their Europe '72 album.
Live at the Fillmore East by Frank Zappa & the Mothers of Invention. (To me, this album is essentially one song). When Bwana Dick speaks, the heavens will part!!!
“Stairway to Heaven” the version on the film The Song Remains the Same by Led Zeppelin
“You Can’t Always Get What You Want” the Rolling Stones. What the hell, it’s close enough to 8 minutes and it’s one of my favorite Stones songs
“Sweet Jane.” Lou Reed’s live version. I only have this on a tape I made myself so I’m unsure of its legnth, but I think it’s about 9 minutes long. A great performance, regardless.
“Taxi” by Harry Chapin
“Alice’s Restaurant” by Arlo Guthrie. (Okay, it’s technically folk, but a lot of rock stations like to play it at Thanksgiving.)
“In the Gadda de Veda” by Iron Butterfly
“Superwoman” by Stevie Wonder
“Nights in White Satin”/the epilogue poem by The Moody Blues
“Lily, Rosemary, and the Jack of Hearts” by Bob Dylan. “Tangled Up in Blue” is a better song, but it’s shorter.
“Sad-Eyed Lady of the Lowlands” by Bob Dylan
Tool - Reflection is really good. As is Third Eye.
What a non-specific question… One runner-up could be Sonic Youth’s “The Diamond Sea”, which clocks in at almost 20 minutes. Spacemen 3’s “Suicide” and Television’s Marquee Moon are both great and about 11 minutes long. “Krautrock” by Faust is a damn nice song, too. “Hallogallo” by Neu! is a great song at just above ten minutes, and I think Stereolab borrowed a little from it for Jenny Ondioline. 
But the winner has to be “Soon” by My Bloody Valentine. It’s IMO one of the best rock songs ever, and thus also one of the best 8+ minute-long rock songs ever.
Oh, and I forgot one. SISTER RAY!!!
*oh but I haven’t got the time-time
hey, hey, she’s busy sucking on my ding-dong
she’s busy sucking on the ding-dong
aww, now, just like Sister Ray says
*
Isn’t “Stairway to Heaven” more than 8 minutes long?
Opeth - Advent 13:45
How long is The Day the Music Died?
And by “The Day the Music Died” of course, I mean “American Pie”
(talk about brainfarts.)
Oh, so many…most of the songs I listen to are >8 minutes in length!
Spock’s Beard
[ul][li]“At the End of the Day” (16:28)[/li][li]“The Great Nothing” (27:01)[/li][li]“Harm’s Way” (11:06)[/li][li]“Flow” (15:48)[/li][li]“The Doorway” (11:27)[/li][li]“The Healing Colors of Sound” suite (live - 20:00)[/li][/ul]
Transatlantic
[ul][li]“All of the Above” (30:59)[/li][li]“Duel With the Devil” (26:43)[/li][li]“Suite Charlotte Pike” (14:30)[/li][li]“Stranger in your Soul” (26:05)[/li][/ul]
Dream Theater
[ul][li]“Home” (12:53)[/li][li]“A Change of Seasons” (~20:00)[/li][li]“Metropolis Part I” (9:30)[/li][li]“Lines in the Sand” (12:05)[/li][li]“Six Degrees of Inner Turbulence” (42:02)[/li][/ul]
Yes
And You and I
Just barely, at 8:03.
I nominate Nile’s “Unas, Slayer of the Gods” and Opeth’s “Black Rose Immortal”.
Something Corporate’s Konstantine, which is 9.35. I adore it, after having listened to it 400 times in three months.
“The Decline” by NOFX. It clocks in at over 18 minutes.
It was on its own one song EP, which they advertised as “One song too long”.
The Stooges: “We Will Fall.”
Paradise By the Dashboard Light - Meat Loaf
(clocks in at just over 8 minutes…)
Another vote for “Third Eye” by tool.
Yeah, Monstre!
I’ll also nominate Jungleland - Bruce Springsteen
I do just have to say that I have a hard time really liking a song that is minutes upon minutes of jamming and soloing over the same chords. It’s like a jazz tune where the actual song is 1.5 minutes, and you just play over and over and over again.