A rare Leica recently sold at Auction for almost $3 million - the most amount of money ever commanded for a camera. This Leica, which was made in 1923, was a '0 series'; a prototype of the Leica A which was launched 2 years later. Out of 25 produced, only 12 are still known to exist.
Without doubt Leica remains the most collectable camera brand in the world, and is able to command huge premiums over significantly better cameras in whatever generation you choose.
The below was shot with a Leica IIc, a direct descendant of Oskar Barnack's original; with a Leica 50mm f1.5 Summarit.