Now discontinued, but if you are lucky, you can still purchase a 645 Pro TL (this model's successor). Even newer models to this are the AF & the AFD (Auto-Focus with easy digital capability).
The 645 Pro is a modular medium formatcamera (unlike the 645E). Not only are the lenses interchangable, but the viewfinders, winders, and film backs are also. Lenses (and film inserts) dating back to the 1970s work perfectly on the 645 Pro, other accessories (viewfinders, etc) need to be intended for the 645 Super (or the 645 Pro TL) to fit the 645 Pro.
The horizontally traversing cloth shutter gives a shutter speed range of 4 secs - 1/1000th sec & B, with the flash sync speed being 1/60th sec ("leaf-shutter" lenses will allow flash sync at speeds of up to 1/500th sec). Two of the available viewfinders allow the camera to offer aperture priority metering (one of these finders also allows spot metering).
The camera can use 120, 220, 135 (35mm), and Polaroid film. 120 film will give 15 exposures to the roll, 220 gives 30 (but is harder to source), the amount of exposures given by 135 film will depend on the length of the film. Polaroid film is generally used to double-check exposure and composition. The beauty of removable film backs means that a different film can be used before finishing one that is currently being used.
Build wise, the 645 Pro feels solid. Being a medium format camera, it is not lightweight. When fitted with one of the motor-winders & a prism/mirror viewfinder, the camera handles much like an oversized 35mm (but, with a massive viewfinder image).
If using 120 (or 220) film, the quality of the images is fabulous. Extreme enlargements/crops can be easily achieved. I've only printed up to 10"x8", but I have cropped some images so that only a small portion of the negative was used (if I'd used the full frame, the pictures would have been in excess of 16"x24").
Other funtions that this camera offers are; multiple exposures, mirror lock-up, & self timer.
All in all; a great camera, the lenses are super-sharp. At current secondhand prices, it's a steal.