I'm afraid I'm with Prawn On The Cob (and of course, Balto) here, i really do think the Viper ACR has the makings of a future classic. As stated before, it's a fresh design, and, being the top-of-the-range model, is the most desirable.
The ZR1, has an inkling of a chance perhaps, if only because it's the first Corvette that can properly give a Lambo a bloody nose (search autocar.co.uk - ZR1 vs LP670). Problem with the 'Vette though is that it's not really groundbreaking in any way.
Audi R8, definitely will be a future classic: Being Audi's first proper supercar is one thing, but actually being bloody good just raises the bar a couple of notches. Again, it's a fresh concept (from Audi in any case), and being the flagship model with much better performance than everything else in the range, is once again the most desirable.
Same can't be said of the Ford GT and BMW Z8 though. Is it possible for a retro design to ever be a classic? If someone does it again in 40 years time, will it make that a retro-retro design? I'm not sure. If there is a chance of retro achieving classic status though, my money would be on the Z8, chiefly because it was a limited edition, and had screentime in a James Bond film.
CTS-V? Bah. Supersaloons have almost zero chance of being a classic unless 1) they were featured in a big-budget film (Audi S8 from Ronin perhaps), 2) they were the first of their kind (BMW E30 M3) or pushed the performance benchmark to absurd levels (Vauxhall Lotus Carlton). The CTS-V pushes none of those buttons.
Same for the Magnum. Like, wtf?
The Prius will be remembered, but like everyone said, probably won't be a classic. It's not revolutionary enough. It hasn't had a big enough impact on contemporary culture. It's not even universally liked. Yes, it is the granddaddy of the "green" movement, but since when has that sort of thing excited people?
Porsche Carrera GT: Probably will be a classic. Firstly, it's a hypercar, which obviously helps. Second, it's unique in being a mid-engined Porsche, and the h-a-l-o (stupid forum auto-censor) model no less. Third, it came out around the same time as the Enzo and McMerc SLR, so for most, they'll probably remember those cars together as the ones who kick-started the noughties' hypercar frenzy (of course resulting in such metal as the Veyron, Reventon, CCX, S7 etc)
Honda S2000? Maybe, just maybe. Came out during a dry spell in the roadster market, and could be credited as having kick-started the class again. Of course, it has a unique selling point, in the manic 9000rpm VTEC engine, as well as the digital tacho. We don't realise it now, because it's so common, but 20 years down the road, i do think we'll remember it really fondly
*whew* that was probably my longest post ever :p