One morning when I was in college, my clock radio alarm went off at some early hour with the opening riff of Jethro Tull's epic "Aqualung" (Duh-duh-duh-duh-duhhh-duhhh!). I hit snooze, and five or six minutes later the alarm went off with the same riff, thankfully letting me sleep through the flute solo. Some songs are just long like that.
"Aqualung" is a little self-indulgent for my taste, but "Cortez the Killer" by Neil Young is one of my favorite really, really long songs. What are yours?