Wow, this is very difficult because there are so many that I enjoy for so many reasons but I'll do my best to pick just 5...
Pink Floyd- Dark Side of the Moon, I have to have a Floyd fix and honestly, to me, this album is a masterpiece when it comes to concept albums.
Bob Dylan- The Best of Bob Dylan, So many great songs to choose from for any given mood.
Stevie Ray Vaughn- Greatest Hits, Virtuoso guitar & rocking blues. From his covers of songs like "The Sky is Crying" to his classic "Pride & Joy"
Janis Joplin- Pearl, just because, well, Janis. Nuff said.
T. Rex- The Slider, sometimes I just need escapism and Marc Bolan's weird and wonderful style takes me away from it all in my mind. Metal Guru is one of my favorite tunes ever.
There's about 10 other albums that could easily supplant these but for today, these have to be my choice.