I think all Rollei TLRs and Rollei SL66. Prices of good SL66 stuff are already going up. Used Hasselblad V cameras can be had for very reasonable money today, but they are destined to become classics without a doubt. Canon EOS 30/Elan 7 is one of the most sought after EOS cameras. I think they will become classics too.
Fuji folders and large 6x9 rangefinders. As they are still making the smaller mf folders the big rangefinders are unique and only dated from the 80s.
Any Chinese camera, as that economy is steaming on, over time there maybe a large market of collectors who would want Chinese made cameras because of national heritage, or the handwork that goes into some of them. The large format cameras and medium format slr's and tlrs such as from seagull.
There is already a large collectors market in china for art and luxury goods, outside of china strong national brands such as seagull have a small market of collectors for other items such as watches of the higher calibers or kitsch design . This could be the same for cameras in time such as Russian cameras.
With the trend in the way people capture and print images, if a camera isn't already considered a classic I doubt it will obtain that status in the future.
I'm surprised that nobody has mentioned the Canon T90 that although only manufacture for a short time it was the design and concept that nearly all the subsequent modern 35mm S.L.R.s both film and digital ones are based on. http://en.wikipedia.org/wiki/Canon_T90 Before 1986 S.L.R.s didn't look like that.
I would include the Canon A-1 in this category. I've owned one for 30 years now. Still a very enjoyable camera.
How about the Nikon F100 and the Contax 137. The Nikon, although autofocus, was an excellent marriage of the electronic everything, yet still was a good, reliable workhorse instrument. The Contax, with built in motor drive, Zeiss lenses and auto exposure has been one of my favorite machines for speed, weight and mobility in the 35mm universe.
1. I think it has a very classic appearance.
2. Its innovative small size and lightweight was so popular that it influenced other manufacturers to copy.