$6.95 hand reg -> $2,100 sale within 12 months is my best gain so far.
$225 -> $575 within 24 hours is my quickest gain of consequence so far.
Had another domain (tobaccotogo.com) for sale for $40 in a thread here, when I got a NSI certified offer which translated into a $750 sale. That's probably my closest near miss.
Biggest loss (someone else's success story -- but I'll tell on myself before they get a chance) was chubby.org last December. Sold it for a mere $25 or something in a big domain sale, and the buyer turned around and sold it right here on DNF for $400+. Misjudged that one, I guess.