After having had great fun reading the Asimov short story "The Last Question" (posted by archaic_architect to the Hyperspace Tavern), I thought I'd also share a story which was (and still is) really precious to my heart.
I first read this one when I was 12, and it had an immense impact on me. I remember closing myself up in the bathroom with a candle, meditating on the center of the flame, dreaming of the super-powers this would give me if I persisted.
Find the story attached in a 47-page PDF, extracted from a file I've found on 4shared.com.
Enjoy.