Personally, I have to go with Eminem's "Beautiful". I was depressed at one point in my life and I can definitely relate to the lyrics of that amazing and thoughtful song.
I can relate to these songs atm:
"Beautiful" and "Not Afraid" by Eminem
"Goodmorning" by William Fitzsimmons
"Can't Help Falling In Love" by Ingrid Michaelson
"Pursuit of Happiness" by Kid Cudi ft. MGMT and Ratatat
Drake - Find Your Love
BEP - Meet Me Halfway
I Miss You - Miley Cyrus (shut up...it really personifies the emotions I feel whenever I lose someone close)
Airplanes - B.o.B.
If We Ever Meet Again - Timbaland (one of my friends I kinda liked moved away...)