Most 'surprising' camera?

Smena 8m. Soviet plastic, fully manual operation, sharp lens. Sharp.

Agfa Clack

Pentax MZ-S. A start from scratch design that gets it right.

I know it's a really good camera, but the camera that surprised me the most was my F100..now hear me out:

I had an FE and an N80 before that and never really got good images out of them. It seemed like everything looked muddy and my negs were thin. It really turned me off of film because the images looked so bad. It seemed like it was always a crap shoot when I used the N80. I sold it, shot digital for years, then got my hands on an gripped F100 and SB26 for $75 (it was covered in Coca Cola). Cleaned it up and found out that aside from the soda it was in great shape. Shot of a few rolls of that, and I don't know if it was the light or the metering, but the images looked GREAT. Punchy, clean, detailed, totally different than my N80. Since than, I don't know if it's confidence, or something else that's psychological, but that F100 is what really surprised me with what film could do and really helped me be confident in taking my business into a film workflow.

Rolleiflex 3.5

A Rolleiflex Automat 3.5 (type 4) I picked up a few weeks ago at an out-of-state estate auction (for $70 US). I ran a roll of Plus X b&w through it at an arts and music festival in North Carolina, and I was very pleasantly surprised at the resulting photos.
The camera is kind of battered externally, but the glass and shutter are fine, obviously.
The Rolleiflex is very portable compared to the rest of my medium format menagerie, so I think I'll take it out more. I'll try Velvia next.

Mamiya RZ67 Pro II managed to surprise me when I shot TMX - the light and contrast through the image was brilliant, detailed, complete. My current surprise is the flexibility of a Canon EOS 1V - this is the last camera for film Canon will be making, it's a fully professional modern SLR, the exposure of black and white under almost any condition is very good, autofocus is blindingly fast, the camera is close to perfect. And these 1800.00 cameras are available for 400.00 used in excellent shape. Drop back to a 1N and it's 140.00...

Nikon Lite Touch AF/AF600. Small, light, fast accurate focus, quiet and with a fantastic 28/3.5 lens. Why this camera is not a cult-classic like the Olympus Stylus Epic and the Yashica T4/T5 is beyond me, it is an absolutely wonderful little camera.

Tough. I've had a number of cameras and each was so good. Part of the answer depends on the expectation at time of purchase. I guess the Leica CL which is a favorite would qualify as when I bought it I knew all the negative feelings about it from Leicaphiles. Not a real Leica, etc. I bought it not so much because I wanted it but as a favor to the prior owner who was a friend. I had my eyes of a M series such as a 4. However, it turned out to be a real Leica in the truest sense along with one of the best Leica lenses, the 40mm Summicron-C. I've since tried and handled M series cameras and they are too heavy and too big. I'd have to go back to a SM Leica to be happy.

Another more plebian camera is the Vito B, currently in need of a shutter cla. Picked up at a flea market along with the Ikonta 35mm folder likewise now needing a cla. The Color-Slopar lens of the Vito is just so wonderful, especially with transparency film such as the old Kodachrome. For some years whenever I wanted to shoot transparency film, it was the camera of choice. When I got it I had not idea of it except it was like new and cheap. The Ikonta folder was for some years my pocket camera. The lens while very good does not have the magic of the Vito with color film but load it with Tech Pan and leave all else at home, especially when going to develop the Tech Pan as a continious toanl film rather than high contrast. A near perfect mating.

For me I think it is my Gakken stereo pinhole camera. These are plastic kits that come with a magazine from Japan. I got it as a gift and I really didn't know what to expect. I found that it is actually very well designed and the plastic parts are of a much higher quality than any toy cameras I've used, such as a Holga. It works well and produces some very interesting images, both stereo and "mono". Fun.

Without a doubt the Voigtländer Vitessa "barndoors" with Ultron lens. Technicaly strange and unique but I like the ergonomy very well!! and lens is gorgeous!!! Closed it's (nearly) a pocket camera. It's build like a tank, film advance by plunger seems strange first but nice to use.
I really like the focus dial on the back (same as on early Fujica rangefinder).

Far bigger, also technicaly unique and also with fabulous lens, the Kodak Medalist!

These are my favorite and most surprising camera.

For medium format, I'm always surprised when I pull out the old Mamiya C33. It's such a basic, featureless camera compared to my other bodies, but it always seems to take a spectacular photo.

For 35mm, it's not entirely unexpected considering the body, but I do like to use the old F4 every now and then. I've gotten used to the F6 now, but I'm always surprised at what the F4 is capable of. There is no LCD display, no fancy programs, only one AF area, no VR, but the exposures are always perfect (unless there's some sort of user error!)

Most surprising camera: the box camera I got when I was a young child, about 6 years old or so. The cost? $1 and two cereal box tops. The surprise was my mother's. She, being a skeptic, had said "they will never send you that camera", but they did send it, and it was my first camera of a long on-again-off-again love affair with photography.

Not sure if this counts, being a 'Frankencamera' - but I bought a folding 6 X 6 roll film camera off eBay. It looked ok in the eBay photos (don't they always) but it was a bit of a lemon. The shutter was a box camera like affair and the lens a plastic meniscus, cloudy and scratched. Very nice body, though.

A friend gave me some shutters. A small pronto press shutter came with a Steinheil 55 mm lens in it. I expected the lens to be useless but when I looked at it - there was something compelling and unusual about it. It was mint, fully multi-coated and rather physically small - but also seemed to have an air spaced symmetrical construction. Unsure of why a 55mm lens would be in such a shutter anyway - I mounted it, crudely, on the 6 X 6, just as an experiment. I wanted to see how big the image circle was, expecting it to cover 35mm.

The first roll through it blew my socks off! The lens seemed to cover 6 X 6 with no discernible light fall off or lack of sharpness at the edges and had biting contrast. It seemed to easily out perform some of the classic folding 6 X 6 cameras I have with their original optics. I still can't quite come to terms with how a 55mm lens that physically small can cover so much so well. I am now in the process of deciding how to mount it better on the camera to make it easier to focus.

I like the results I get with all of my cameras, even the garage sale bargain cameras I have purchased!

The two most surprising cameras I have are my Pentax Super Program and my Minolta 400si. The images I get with them are sharp, great color saturation and very well exposed.

Of my Nikons, my favorite bargain camera is definitely the N80. While not as robust as my F100, the N80 is a spectacular light weight camera. My only issue with it is that I chipped the top LCD screen some time ago (entirely my fault), and I really don't want to buy a new body (I doubt it can be fixed and it would probably be cheaper to get a new body).