Actually, you are far from being right. There are songs that go on for way longer.
The longest song ever made by a real band is, most likely, Found A Star On The Ground by The Flaming Lips. It is 6 hours and 19 seconds long. That's right, it goes on non-stop for 6 hours. I don't know if there are longer songs, but that may be the longest song by a somewhat well-known and well received group.
There are other songs that are very long too. Brian Eno's ambient works "Thrusday Afternoon" and Neroli both go on for a hour, and "Discreet Music" goes on for a half-hour. Tangerine Dreams "Ricochet" is around 40 minutes long, counting both sides, LCD soundsystem made "45:33", which is actually 46 minutes long and 5 seconds.
Prog-Rock bands have a habit of making really long songs. Emerson Lake and Palmer's Karn-Evil 9 goes on for 30 minutes (although there are seperate tracks for the suite). Jethro Tull's "Thick As A Brick" is 40 minutes, if you count both rides. Other long songs are Supper's Ready (Genesis), 2112 (Rush), Echoes (Pink Floyd), Gates Of Delirium (Yes), Change Of Season (Dream Theater), Plague Of The Lighthouse Keepers (Van Der Graff Generator) and Tarkus (Another Emerson Lake And Palmer song) are all around 20 minutes.
So, there. I don't know what the Top 3 longest songs ever are, but i would say Found A Star On The Ground, clocking at 6 hours, would be the longest recorded.
Oh, and just so people know, Stairway To Heaven isn't even Led Zeppelin's longest song. Their longest studio song is "In My Time Of Dying" from their classic Psychical Graffiti album. The song is 11 minutes long, about 3 or 4 minutes longer than Stairway To Heaven. The longest song that was on a album was the live version of "Dazed and Confused", from "The Song Remains The Same." It goes on for 26 minutes and 53 seconds.
There. You know now the longest songs of all time. You can go live your life happy now.