Not so much the classic albums as such, but those individual songs/pieces that stand out to you, and why. A few starters for my part -
Con-Dom, "Moors Rapist". Any track that has the chorus "women need rape" is going to stand out, but this is a driving, pounding thing of instant musical attraction. It builds slowly and sustains its tension throughout the piece, and the angry misogyny of the lyrics expose more of the mind of men than the mere words. I used this piece as an example when explaining to my sister the complexities of PE.
Brighter Death Now, "Fourteen". For similar reasons as the previous, this is a genuinely disturbing piece, the slow, sinister build-up towards the ultimate atrocity followed by footsteps leaving the school to anonymity and freedom, Karmonik's final admonition - "You're fourteen...you're mine" remains ringing in the mind. Psychological aural cinema.
(I'd also offer "Now Is The Time", as that piece really jumped out at me when I heard it for the first time. I was rather hoping that it would be one album-long track, but that would be a vocal gymnastic miracle).
Genocide Organ, "At Judas". This piece always stood out for me. The slow, restrained pound of the rhythm, the slow, restrained oscillation of the synthesiser, the mystery of the simple vocal refrain. A piece that offers no answers but inflicts great emotional impact.
Deathpile, "You Will Never Know". The final blast from one of PE's highlight albums, the lyrics brilliantly get the to the core of murder/serial killer obsession. The un-answered questions that are never resolved, that remain to haunt and harm those who ponder, all rendered in Canady's full-throated, hate-filled roar. Maximum impact, US PE at it's peak.