I've had a gander at my collection and, discounting some krautrock here and rave music there, you can trace quite a linear progression throughout the ages. Starting with British post punk of the late 70s and early 80's, going into glossy synth pop at the end of the 80s, crossing the pond with North American grunge and indie rock throughout most of the 90s, going into more folky, lo-fi stuff at the turn of the century, then fragmenting in the 2000s, splitting between biggish 'Merican indie rockers and weird electronica/ambient stuff.
That's a bit too narrow, but a good overview of where my interest lies. However - I have been able to pinpoint two records that stand out as quite unlike anything else in my collection.
1) SND - Atavism - http://www.youtube.com/watch?v=-HK5AKL0_XI
IDM without much 'D'. It's so clinical and harsh throughout. Little bass, just piercing treble. Occasionally suggests a rhythm, only to fragment again. Contains some tracks only a robot could love. But I still listen; it's completely intriguing - it gives me a headache but when i'm in a certain mood I really really like it.
2) The Locust - Plague Soundscapes - http://www.youtube.com/watch?v=RpLmTAFk9LQ
Again, I put this on once in a blue moon, usually when very very angry. I've no real interest in exploring the grindcore genre further - this is all I need.
What records stand out in your collection that are singular and unique to the rest?