One of the bands that helped introduce me to grindcore (and extreme metal in general) are England's mighty Bolt Thrower. I really lucked out and picked up first presses of both Warmaster (1991) and the gatefold edition of Realm of Chaos (1989). Both records are absolute masterpieces of their style and arguably their best material.
'Realm of Chaos' had the original lyrics booklet featuring the lyrics aside artwork taken from the world of Warhammer 40k, obviously a massive inspiration on the band. For closeups on select pages see below. The dark unforgiving world depicted really adds to the whole experience of the band and the original artwork is infinitely better then the recent CD release. For an interesting read as to why they had to change the artwork and how the band feels about this (VERY displeased) read the Ask Earache blog here.