An Alien God I now regularly refer to evolutionary forces as Azathoth, it helps clarify the thinking. And it gives me a Power to fight against (a strong motivator for my psychology)
You Only Live Twice finally got me signed up for cryonics. As such, it has likely saved my life.
Yehuda Yudkowsky is still one of the most touching things I've ever read. I very rarely cry.
The Sword of Good got me to fundamentally re-order how I evaluate what is Good.
What's still on your mind (in a positive way) a year or more after it was posted?