Oh dear god, this is a topic I could opine about for pages upon pages. So, instead of boring the shit out of everyone, here are some specific songs that carry specific, lifelong meanings for me.
"Landslide" by Fleetwood Mac, specifically the reunion tour version. This song was my Year 1 theme after coming out when I was 19. Despite how much I hate the show, I was pleasantly surprised to hear it got busted out as Santana's coming out song on Glee. (BTW, Jacien, I love how 'Bootylicious' uses Stevie Nicks' guitar riff from 'Edge of Seventeen'!)
"Battle with the Four Fiends" from Final Fantasy IV is my 'get amped up for a work out/fucking shit up' anthem. It's kind of ridiculous how that song can get me so psyched up after 20 years.
"Know Your Enemy" from Green Day will forever remind me of when I was the most angry and pissed off I've ever been. I had this on repeat after Prop 8 passed in California and it's my song for when I'm done with the idiots of the world.
On a slightly related note, I ended up singing "Will the Circle be Unbroken" from Bioshock Infinite last night in my room, spurred on by the Boston Marathon bombings. There's a sweet melancholy to that song, especially in its reworked version.