Flexaret and Flexpar closeup lenses
I've been using a Flexaret VII for a while and been quite happy with the images although they have been a little 'flat' in terms of contrast.
However, recently, I picked up a yellow filter and a couple of sets of Flexpar closeup lenses for it (with the built in prisms for parallex correction) and I've been blown away with the results -- both the higher contrast with the filter and the lovely look of images shot with the closeup lenses.
These are from the first roll I shot and have been scanned straight and then just given a slight levels tweak and sharpening. No heavy changes at all -- these are pretty much as is.