A friend of mine used to play the Smashing Pumpkins song "Drown" every time we went to a certain bar in our college town. He did this because 1.) the three minutes of guitar feedback really irritated people (this is back when most people who even knew who the Pumpkins were thought they were from Seattle), and B.) he felt like he was getting better value for his dollar, since it was one of the longest songs on the jukebox.
First up on my work version of iTunes: "Her Lips Were Wet With Venom," the Sunn O)))/Boris/Earth collaboration (which makes the Pumpkins' tune seem like DK's "I Like Short Songs" in comparison)—clocking in at a cool 28:14. What's your longest?