xx by The xx - we wouldn't have James Blake, which means we wouldn't have Lapsley or the stylings of many modern artists without this
New Forms by Roni Size - when this came out we said "okay drum 'n bass is done, there's nothing left to do!"
Is This It by The Strokes - kicked off a long era of modern indie rock IMV
Joshua Tree by U2 - a classic for pop-rock
Graceland by Paul Simon - a jewel, classic of pop-fusion
Sgt Peppers by The Beatles - could have picked Revolver, White Album, Abbey Road ... you get the idea
Kind of Blue by Miles Davis - not as cool, or good, as Bitches Brew but this is the definitive jazz record IMV
Well-Tempered Clavier by Bach - this a work, but there were no albums back then - he's the grand-daddy
These aren't my top 8 albums/works, though I do love them, but IMV these are "important" for their genres - which I think is the question.