Oh, I have so many!! But my #1 song is Breathe In, Breathe Out, Move On by Jimmy Buffett. It's such a healing song, and it helps me so much.
Other ones that mean so much to me are:
Letter to Me - Brad Paisley
Constellations - Jack Johnson
Awake - Josh Groban
Laughed Until We Cried - Jason Aldean
Watching Airplanes - Gary Allan
These Are The Day - Sugarland
If you haven't noticed, the theme to all those songs is the good days with friends and family and all the good memories that you made throughout your years. Those songs mean so much to me because my memories of past years are the most important thing I have, and I would NEVER trade them for the world.