Weightless

Scientists in the UK did scientific tests, and concluded that this song is the most relaxing song ever made--so good, in fact, that even Enya can't touch it.  It's a song so powerful, that it lowers brain activity, cuts anxiety, slows your heart-rate, and is even effective at inducing sleep.

Clocking in at a glacial 60bpm, "Weightless" by Marconi Union, is a song that was engineered with sound therapists from the start to be the most relaxing song known to mankind.  Unlike conventional songs, it has no consistent melody, which prevents your brain from trying to anticipate changes in structure.  This unusual decision, along with a host of other tricks that I'm too lazy to explain or understand, come together in a song that is definitely drug-like.