To further what Kuru has said, Polaroid 600-series film and the 600-series cameras would come close to being the most popular range. They are often the cheapest, and certainly have their film still in production. No where near as complex as the SX-70s, reliable perhaps as a result...
Also! Do not forget the Spectra series of cameras, including the 'Pro' series that gives an element of control of the normally full automated functions of the 600 cameras. These take Spectra or 1200 series film. Only one type of 600 and two types of Spectra film is still made I think, though I have seen some 600-series Sepia recently I suspect it was old stock.
Both 600 series and Spectra series cameras can be picked up for a few yen in most second hand places. Along with the SX-70, these are called 'Integral' cameras, as opposed to 'Peel Apart' or 'Pack Film' cameras. All non-integral cameras are called Land Cameras. One of these cameras and its film - the 1200 I think - will remain in production for a while yet as in many locales Polaroid photographs remain admissable in court as evidence.
The pick for collectors of each appear to the either the Lego 600-series, the Barbie 600-series, or my fave the Kitty-chan 600-series (with matching pink carry-case). The Spectra to look for is the Onyx with full set of controls (in a complete set it comes with remote, close-up and tele-lenses and a few other goodies) and a neato smoked transparent case.
There is one more device, but I am keeping that a secret. Skorj.
