Sigma DP2 Merrill
I recently acquired the Sigma DP2 Merrill with the Foveon sensor. While it's technically only a 15 megapixel camera, the resulting images rival medium format digital due to the three layer Foveon sensor.
The DP2 does not look like it would deliver such results. But examining the full size files is an amazing exercise; images are remarkable detailed and require no sharpening. The full resolution image can be downloaded free if you want to see for yourself. Mouse over and click the small button below the image.