Hasselblad 1600F

When: 1948.
Why: First trully modular SLR camera.

Hasselblad cameras are still used by professionals (mostly) and they still have the same modular design - interchangeable everything: lens, back, viewfinder. 1600F was the first camera by Hasselblad (excluding military aicraft models) in their long line of medium format SLRs. These cameras are somewhat expensive, but they offer excellent flexibility. These days you can even get a digital back that attaches to the same film body.

Franke & Heidecke: Rolleiflex Original

When: 1929
Why: First rollfilm TLR (Twin-Lens-Reflex).

Also it's a first medium format Franke & Heidecke camera. Franke & Heidecke manufactured a couple of stereo TLR camera models before (Rolleidoscop), but again, those were stereo cameras, not exactly suitable for the regular job. Rolleiflex Original was an instant success, and became a parent of many more TLR models which are still produced. You can find detailed specs of this camera on the Rollei Club web-site.