Hot Fuss by The Killers, just a really slick, super hard hitting album that captures a lot of feelings I've had in my life.
Def Leppards Greatest Hits by Def Leppard, first album I ever bought.
Rumours by Fleetwood Mac, again, I relate it a lot of my life and it's just a truly wonderful piece of music. It's art.
1984 by Van Halen, my early to mid teens were dominated by this album. I'll always remember the first time I heard "I'll Wait", amazing song.
Hybrid Theory and Meteora by Linkin Park, both quintessential to my childhood and teens.
Core by STP, for reasons I am still uncertain of. Its an amazing album, but why I'm not sure.
More recent ones would have to be Outrun by Kavinsky, Save Rock & Roll by Fallout Boy, In A Tidal Wave Of Mystery by Capital Cities, self titled by The Colourist, and I expect Pop Psychology by Neon Trees to be the same way, just too early to tell. Simply because they've defined my life at certain points, they've been my life soundtrack.