My all-time favourite that I’ve participated in was The Story of a Five-Dollar Biil. Money! Alien invasions! Buxom women! Black helicopters! Demigods! This thread had it all!
Close second were some of the InitiationComplex threads. If you ever wondered where the calamari came from…
I was just thinking about it a month or so ago while watching The Stand on SciFi… for some reason, I was wondering if somebody made a post along the lines of “At least something got that craptacular “Baby can you dig your man?” off the radio.”