Nice thread idea!
Looks like we'll have some common music on our lists.
These aren't in any specific order, just typing them up as they come to mind.
Genesis - Invisible Touch: Probably my first album purchase that was really of my own choosing. I was too young to understand the complex emotional pain that Phil was in when he wrote the album, but I did get that it was emotional and I dug that. I find that it has stood the test of time for me.
Megadeth - Rust in Peace: I saw the Hangar 18 video premier on Handbanger's Ball. It blew my mind. Got the album shortly thereafter, and discovered that Hangar 18 was the weakest song on the album (the rest were even better). I got the tab book (no internet then) and learned most of the songs on the album. I recall sitting down with a metronome so that I could get the hang of the main rhythm riff at the beginning of Take No Prisoners. I can still rip out the main riff to Tornado of Souls.
Led Zeppelin - IV: Not sure what to say. It's just awesome. Best drumming in rock, period.
Joe Satriani - Surfing with the Alien: I was taking lessons when I first heard this. Another mind-blower. It's what got me into tapping technique and learning modes.
Steve Vai - Passion & Warfare: This was, for me, the next logical step from Satch. Kind of like old Joe, but with more emotion (and harmonizer action!). Blue Powder still does it for me, as does Sisters.
Pink Floyd - The Wall: Took me 15 years to come around on this one. I hated it the first time I heard it in high school. Then one night many years later while doing mushrooms, I threw it on for the heck of it (actually, my laptop telepathically suggested I play it). At the end of In the Flesh, I actually hit the deck to avoid being hit by the dive bombing airplane.

I still listen to regularly; it just doesn't get old. Waters is a genius.
Guns n Roses - Appetite for Destruction: This is what made me want to be a rock star. The attitude is as important as the music. Both are raunchy and unapologetic. Ass-kicking rock n roll. I still chase tones off that album.
Wilco - Sky Blue Sky: Probably when I realized that I liked something that didn't feature overlapping distorted tones. Definitely changed the way I thought about my own playing.
Smashing Pumpkins - Siamese Dream: I could actually take or leave all the rest of their albums, but this one is pure gold. And it was the soundtrack to a very formative time in my youth.
The Crystal Method - Vegas: My first "electronic" love. I just really dig the way they put together sounds.
NWA - Straight Outta Compton: The best rap album of all time. Innovative, raw, original.
Green Day - American Idiot: This is their best work. The rest I could probably just leave, but this album is fantastic. Proof that the concept album isn't dead and doesn't have to be overcomplicated prog-rock in 6/8 time. And the broadway show was epic!
Pantera - Vulgar Display of Power: I think this album kicks more ass than any other single album by any artist at any time. The rhythm section is powerful and flawless, and Dime basically invented a new metal genre with his playing.
Rage Against the Machine: The self-titled album was really groundbreaking. Made me learn a whole new approach to playing. And good god the anger! Made me think about politics as well.
Faith No More - The Real Thing: Proof that keyboards are cool in rock bands. I don't think anybody else sounds like these guys, and The Real Thing was their best effort overall, I think.