Bob Dylan
Aint Talking
Tempest
Visions Of Johanna

Fleetwood Mac - Oh Well 9.05

https://www.youtube.com/watch?v=b19PcuJsQbA

How could I forget........
Hawkwind - You Shouldn't Do That 15.41

https://www.youtube.com/watch?v=RhUKB1DK3OE

From the Seminal album Horses

Patti Smith-"Land: Horse/Land of a Thousand Dances 9.25
https://www.youtube.com/watch?v=wssnxfjH-zw

Diamond Head - "Sucking My Love", 9:35.
Status Quo - "Forty Five Hundred Times" 9:53.

Maybe because it's not a very good song. Not in my book anyway.

Nine Feet Underground - Caravan
Eruption - Focus
In memory of Elizabeth Reed (Live) - Allman Brothers
Circumstances - Capability Brown (Queen ripped these off !)

Pyramids - Frank Ocean
What Goes Around... - Justin Timberlake
Untouchable - Girls Aloud

Pink Floyd - Echoes (23 min)
Swans - The Seer (32 min)
Mogwai - Mogwai Fear Satan (17 min)
Sonic Youth - The Diamond Sea (19 min)
Godspeed You Black Emperor - East Hastings (18 min)
Chapterhouse - Die Die Die (12 min)
Sisters of Mercy - Neverland (full version) (12 min)
Spacemen 3 - Suicide (10 min)
Fields of the Nephilim - Last Exit for the Lost (9 min)

and probably about 100 more around the 7-8 minute mark.

Can't believe no one has mentioned Blue Monday (7:29) by New Order. Maybe not the longest, but the biggest-selling 12" single of all time.

The Orb ‎- Blue Room (17:34) from the album U.F.Orb. Have noticed there is a version which is almost 40 mins long, but have not listened to that yet.

Underworld - Rez (9:57)

Can I get away with Tubular Bells?

Also, The End by The Doors...

Oops, forgot to mention Autobahn by Kraftwerk (22 mins)

Massive Attack - Protection

November rain Guns N' Roses

The Velvet Underground - 'Sister Ray' (17'27")
David Bowie - 'Station to Station' (10'14')
Angels and Airwaves - 'Diary' (7'40")

Bon Jovi - Dry County
Metallica - the Unforgiven III (most of the songs on Death Magnetic are long, actually)
Oasis - Champagne Supernova

I like the tracks already posted for Genesis and Caravan.
In addition here's a few that i've listened to most on my iTunes

Peter Frampton - Do You Feel Like We Do (13:43) Live version
Television - Marquee Moon (10:38)
The Velvet Underground - The Gift (10:34)
Gary Byrd & The GB Experience - The Crown (10:31)
Al Stewart - Nostradamus (10:10)