I'd have to agree with the Metallica, Nirvana, Pink Floyd, and Pumpins albums already mentioned. To that I would add NIN - Pretty Hate Machine, Rage Against the Machine - Self Titled, Deftones - Around the Fur, and albums of some lesser known bands that were ground breaking for them, and for me when I heard them: Jimmy Eat World - Clarity; Thursday - Full Collapse; AFI - Black Sails in the Sunset; From Autumn to Ashes - Too Bad You're Beautiful; Social Distortion - Self titled; The Gin Blossoms - New Miserable Experience. This is all that I can think of, for now.