[arlecchino]

6 Degrees of Inner Turbulence - 6 Degrees of Inner Turbulence - Dream Theater - 46 min (on the album it's divided into 8 songs, on the Score DVD/Live Album it's listed as a whole song, and probably longer...)
Stranger in Your Soul - Bridge across Forever - Transatlantic - 30 min
Three Minute Warning - Liquid Tension Experiment - Liquid Tesion experiment - 28:37
Duel with The Devil - Bridge across Forever - Transatlantic - 26:33
Octavarium - Octavarium - Dream Theater - 24 min
A Change of Seasons - A Change of Seasons - Dream Theater - 24 min

out of my 1201 songs in iTunes 161 are 7 minutes or longer
only 489 (just over 1/3) are under 4 minutes. one benefit of listening to prog music

[Rapsodius]

Not sure if it counts, but I've been in a performance of Mahlers 3rd Symphony.
It's 93 minutes long.

Well, I know that classical music is lenghty, but it counts as long as it was the same movement, ie when they stop performing, it's another 'song' or movement (properly)

Shine On You Crazy Diamond, Parts I - IX (26:01)

This may fail on a technicality because the song is broken up into two "tracks" with 3 unrelated tracks sandwiched between, but I have listened to them both back-to-back before.

And this is, of course, Pink Floyd.

Its allright there since it is the same song actually, but splitted

[Ford Prefect]

Not sure if it counts, but I've been in a performance of Mahlers 3rd Symphony.
It's 93 minutes long.

Well, I know that classical music is lenghty, but it counts as long as it was the same movement, ie when they stop performing, it's another 'song' or movement (properly)

It wasn't; it's in five movements. I don't think it's really fair to count classical/art music for this purpose. The longest continuous composition I know is La Monte Young's The Well-Tuned Piano, which, at its longest, runs six hours and twenty-five minutes (and about five hours at its shortest.) But no one would ever call that a "song."

[Lucika]

I had a 14:52:33 version (still remember the number ) of Prodigy - Breath but it turned out in the 5th minute that after the song ends, the rest is silence

[Nuke]

my longest tracks in my playlist which are not length computation errors seem to be all stalaggh projekts, which are essentially black noise and the resulting stimulated mental patients, literally, projekt misanthropia is 35 minutes, projekt nihil is 34:42, projekt  projekt terror is 34:11, of course theese are ambient tracks and dont really count as songs. then there is a song by monster magnet called tab, which sounds a lot like an acid trip, and lasts about as long an 32:14, but i think that was something just designed to listen to when yure high.

now as i get into the real songs which actual structure i got:
Bathory\Twilight of the Gods\01-Twilight of the Gods-Through Blood by Thunder-Blood and Iron.mp3
but according to metal archives this is just the first 3 songs of the album lumped together on an ep which ths appears to be a rip of. metal songs sometimes bleed songs into eachother like this as part of set if they all have the same theme. for example iced earth's gettysburg 1863, which is a 3 song civil war epic consisting of, The devil to pay (12:14), Hold at All Cost (7:08), and High Water Mark (12:35), which mesh together and have the same theme but are distinct songs.

next on my list of long songs is a bunch of ambient tracks:
heres what is arguably the slowest band ever, its actually not bad
Sunn0))) - Decay2 (Nihil's Maw)
recently released from prison, varg vickernes bored the **** out of me with this repetitions repeating of 3 notes on a synth
Burzum - Rundgang um die transzendentale Säule Der Singularität (25:11)
ambient side project of bm band darkthrone, sounds like space noise
Neptune Towers - Caravans to Empire Algol (24:33)
more drone, these guys are actually pretty good
Sunn0))) - Bassaliens (23:22)
more space noise
Neptune Towers - First Communion. Mode: Direct (23:09)

heres some long bm
Countess - Total War (21:19)
and some long prog
Opeth-Black Rose Immortal (20:12)

turns out long songs are nothing special, most end up to either be ambient or filler. or a bunch of stacked tracks, and frankly the replayability falls off after a couple times of listening to it if the songs over around 15 minutes. as for long songs wich totally kick ass (and are over 10 minutes):

Mercyful Fate - Satans Fall (11:28)
Bathory - One Road to Asa Bay (10:24)
Opeth - Deliverance (13:36)
Satyricon - Black Lava (14:31)
The Doors - The End (11:41) (theme song from apocalypse now)
Burzum - A Lost Forgotten Sad pirit (10:52)
Bathory - Shores in Flames (11:09)
Countess - March of the Ten Thousand (11:27)
Enslaved - Lifandi Lif Under Hamri (11:31)
Moonsorrow - Raunioilla (13:36)

[voidSkipper]

Goddamn you've got some nice taste in music, Nuke.

Though I've never been able to get into Sunn o))).

Longest on my playlist...

Dopesmoker by Sleep at 63:31. I hear the original cut was longer, too.
Crimson by Edge of Sanity at 40:00.
Rockets Fall on Rocket Falls by Godspeed You! Black Emperor at 20:42. They have some longer stuff, but this is the only one that isn't packed with ambient and drone elements.
Isolation by Lyrinx at 18:03.

[ShadowsOfLight]

Looks like a few of these have already been mentioned:

Dream Theater - 6 Degrees of Inner Turbulence (41:54)
Dream Theater - Octavarium (24:00)
Dream Theater - A Change of Seasons (23:10)
Rush - 2112 (20:33)
Arena - Moviedrome (19:46)
Rush - Hemispheres (18:08)
Porcupine Tree - Anesthetize (17:43)

All very, very good songs.

[Nuke]

i found another one

Venom - At War With Satan (19:59)

[Androgeos Exeunt]

Ah, how could I forget...?

Beyond The Network - Skaven - Bejeweled 2 - 30:57

[Rapsodius]

turns out long songs are nothing special, most end up to either be ambient or filler. or a bunch of stacked tracks, and frankly the replayability falls off after a couple times of listening to it if the songs over around 15 minutes

Not true, it completely depends on the band's creativity. Specially on prog bands, they change the style on the same song, that never bores, for example 2112 from Rush is 20 minutes long, but the guitar solos, the instruments, vary along time, making it sound quite good, and trust me, it can be replayed many, many times.

It happened to me with prog bands, when you replay a lenghty track, you hear more musical details than the first time, and that's a good attribute, it speaks high of the band, since they can do a very long track, with no limits on replayability.

And BTW, ambience is not considered song here, one could take the white noise sound, record it for 8 hours, and claim that they have the longest 'song'. And with respect with the 3 in 1 tracks, as you said there are actually different songs, so they count, but seperately

[Davros]

All hail the majesty of Prog

In-A-Gadda-Da-Vida - Iron Butterfly (17:02)
Supper's Ready - Genesis (22:54)
Dogs - Pink Floyd (17:04)
Thick as a Brick - Jethro Tull (22:37)
Karn Evil 9 - ELP (29:40)

[Flipside]

Telegraph Road - Dire Straits, 14+ mins. Probably their best ever song.

War of the Worlds - Jeff Wayne - 2 Albums, though, not strictly speaking a 'song', but then many of the tunes mentioned on here aren't songs, there's quite a lot of symphonic writing (not to be confused with symphonic performance) listed above, where several different scores are melded together into one,

[headdie]

Telegraph Road - Dire Straits, 14+ mins. Probably their best ever song.

War of the Worlds - Jeff Wayne - 2 Albums, though, not strictly speaking a 'song', but then many of the tunes mentioned on here aren't songs, there's quite a lot of symphonic writing (not to be confused with symphonic performance) listed above, where several different scores are melded together into one,

WotW truly amazing

[Androgeos Exeunt]

War of the Worlds - Jeff Wayne - 2 Albums

120+ minutes?

[Flipside]

Well, the version I have is on Vinyl from the late 70's, I think each side of those was about 30 minutes, so yup, about 120 minutes

[Androgeos Exeunt]

Sweet

[Galemp]

Well, Floyd, of course, but whenever I see Weird Al in concert I always ask him to play "Albuquerque" at 11:25.

[Nuke]

turns out long songs are nothing special, most end up to either be ambient or filler. or a bunch of stacked tracks, and frankly the replayability falls off after a couple times of listening to it if the songs over around 15 minutes

Not true, it completely depends on the band's creativity. Specially on prog bands, they change the style on the same song, that never bores, for example 2112 from Rush is 20 minutes long, but the guitar solos, the instruments, vary along time, making it sound quite good, and trust me, it can be replayed many, many times.

It happened to me with prog bands, when you replay a lenghty track, you hear more musical details than the first time, and that's a good attribute, it speaks high of the band, since they can do a very long track, with no limits on replayability.

And BTW, ambience is not considered song here, one could take the white noise sound, record it for 8 hours, and claim that they have the longest 'song'. And with respect with the 3 in 1 tracks, as you said there are actually different songs, so they count, but seperately

im not really into prog that much. nor am i into ambient. most of the time i stick to black, death, doom, and thrash metal (on occasion some power and goth metal) which sometimes has its lengthy tracks. prog to me is just too wanky with too much intellectual smug attached and odd time signatures that give me a ****ing headache. long tracks are pretty much a signature of prog (in the same way that very short tracks are typical to grindcore). still rush is a band that earns a great deal of respect from me (though not so much play time). but you put enough solos in one track its length can quickly add up.

[Androgeos Exeunt]

I don't like metal. My preference slants towards songs that fall under the "game" and "soundtrack" genres.

[Nuke]

thats all a bunch of crappy synth