As I have accumulated older interesting cameras. I have also collected a number of viewfinders, mostly older, though one or two are newer.
Nippon Kogaku (Nikon) zoom viewfinder 35-135mm - This one is perhaps my favorite, its a zoom veiwfinder with focus. It's super cool and I still have the original leather case. Voigtlander sells a new wide angle one (15-35mm) for over $500!!
Canon 35mm - This one is likely off a Canon P series as the later 7 had the wide angle range finder. Its useful for using the Leica M3 with a 35mm lens with no 'goggles'.
Voigtlander 21mm - This came with the 21mm f4 lens I have. As I have mostly used this lens on the NEX I have hardly used the viewfinder.
Yashica Tele-Wide finder - Actually I am not 100% sure who made it, but it is likely Yashica, though a similar one also can be attributed to Petri and Tamron. It has two frames, one for 35mm and the other for 70mm, which I gathered by comparing the focal lengths with the D600 fitted with a zoom lens.
Leica 50mm (SBOOI) - A bright viewfinder most likely to designed to be used with a Barnack LTM Leica which generally have dim viewfinders. One reviewer described the launch of this finder as a "masterstroke for Leica". I also have the original case for this too.
Leica 5cm, 9cm, 13.5cm Sports Viewfinder (RASUK / ROSOL) - This is a very cool and unusual non-optical viewfinder. Basically 3 collapsible parts spring up, at the front for the eyepiece and pehind, for the 5cm and 9cm flap, and another for the 13.5cm flap. The eyepiece slides up and down according to subject distance to correct for parallax error.