Great thread. I've got a number of albums to add to the list.
From the "stuff you've probably heard of before" category:
Rush - Moving Pictures, Grace Under Pressure, Hemispheres, Clockwork Angels
Pink Floyd - Wish You Were Here
Led Zeppelin - The Song Remains The Same
AC/DC - Powerage, Back in Black
Black Sabbath - Sabotage
Aerosmith - Toys In The Attic, Rocks, Rock In A Hard Place (extremely underrated album, no doubt to the the lack of Joe Perry)
Yes - Close To The Edge, Going For The One, 90125
Fleetwood Mac - Rumours
Emerson, Lake, and Palmer - Brain Salad Surgery
Tool - 10,000 Days, Lateralus
Jane's Addiction - Ritual De Lo Habitual
Jefferson Airplane - The Worst of Jefferson Airplane (a compilation, but a damn good one)
U2 - War
Trevor Rabin - Can't Look Away
Jethro Tull - Thick As A Brick, Warchild, Minstrel In The Gallery, Songs From The Wood
Iron Maiden - Piece Of Mind
Guns N Roses - Appetite for Destruction
Genesis - A Trick Of The Tail, Wind And Wuthering, Selling England By The Pound
Neil Young And Crazy Horse - Weld, Live Rust (both live albums)
Pearl Jam - Vitalogy
Soundgarden - Badmotorfinger, Superunknown
Pete Townsend - White City
The Who - Who's Next, Quadrophenia
REM - Life's Rich Pageant
Styx - Equinox
Montrose - Montrose
Van Halen - Fair Warning
From the "who the hell are these guys?" category:
Drive-By Truckers - The Dirty South
Riverside - Rapid Eye Movement, Shrine Of New Generation Slaves
Gazpacho - Night, Tick Tock
Glass Hammer - Perilous
Arena - The Visitor
Big Big Train - The Underfall Yard
Ayreon - The Theory Of Everything
The Flower Kings - Space Revolver
Marillion - Script For A Jester's Tear, Brave
Kerry Livegren - Seeds of Change
Porcupine Tree - Fear Of A Blank Planet
Steven Wilson - The Raven That Refused To Sing