Behind all the crazy plot twists and dreamy doctors is "Grey's Anatomy"'s music. The drama and the show's music go hand in hand, to the point that you can't hear some songs ever again without thinking of the "Grey's Anatomy" moment that went with it. As the music supervisor of the show, Alexandra Patsavas has as much to do with fitting the soundtrack songs, and introducing many in the audience to great new music, as the drama that they were paired with. 

"The Quest" - Bryn Christopher. This song served to sum up all of season four as it played over the final scenes of the season. The lyrics, "What I'm gonna live for, what I'm gonna fight for, who you gonna fight for?" is a perfect counterpoint to the Chief making good with Meredith and Adele and the rest of the cast's pairings coming together during a lot of make-out make-up sessions the audience had been dying to see. 

"Chasing Cars" - Snow Patrol. Izzie grieved over her lost beau Denny as this melancholy tune gently blanketed the scene, and it quickly became one of the quintessential pieces of "Grey's Anatomy" music, and inspired not only dozens of fan videos online, but was included in the musical episode.

"On the Radio" - Regina Spektor. Spektor's voice lends a throaty youthfulness to this overall playful, yet philosophical, song, and it works terrifically to capture the energy of a first kiss. In this case, the first kiss was between Finn and Meredith and is a great accompaniment to the rakish qualities of Finn's character. 

"Breathe (2AM)" - Anna Nalick. This was another song chosen to be covered by the cast in the musical episode of "Grey's Anatomy", and while the rendition in that episode was fine, the moment it was paired with just can't compare to the song's original appearance in the show. There haven't been many more intense scenes that when Meredith had her hand in some guy who had a bomb in his chest.

"How to Save a Life" - The Fray. Probably a perfect summation of the entire "Grey's Anatomy" series, or really any hospital show, this piece of music first appeared in the episode "Superstition", when Derek, the Chief, and Burke work to save Denny on the operating table. It soon became the unofficial anthem for the show, and was, of course, sung by the whole cast during the musical episode. This piece of "Grey's Anatomy" music became so iconic with the show that The Fray actually made an alternate version of their music video for this song featuring clips from the show.