This is really tough, and it mostly depends on my mood, but I always go back to these 5:
Cello Suite No. 1 in G Major
It's just one of the most beautiful compositions ever.
Tears For Fears - Everybody Wants To Rule The World
I grew up in the 80's and this captures that feeling perfectly. One of the best summers of my childhood was set to this song.
Queen - Bohemian Rhapsody
Just a timeless classic.
Nirvana - Breed
To me, it defines the 90's along with Smells Like Teen Spirit. This song doesn't get as much love, but I listen to this whenever I want to go back to that time in my life.
Jay-Z & Kanye West - Ni**as In Paris
One of the hardest beats in Hip-Hop imho. I bouce between this and
Tribe Called Quest - Scenario,
Beastie Boys - Intergalactic,
Wu-Tang Clan - C.R.E.A.M.