The mirrorless crowd is probably the best off of digital users in this regard, since due to short flange distance they can utilize stuff like rangefinder lenses, Pentax 100 or even C-mount lenses (sensor coverage not guaranteed :).
In the digital SLR land, Canon has one of the shorter flanges, M42->EF, OM->EF and F->EF adapters are pretty commonly used. Nikon SLR's can't really mount anything other than Leica R lenses without losing the ability to focus to infinity.
Of the stuff David mentioned, I'm not sure about Topcon, if I remember correctly these don't have a focusing helicoid, which would then have to be a part of the adapter (I could be mistaken though).
Listing of flange distances for a big chunk of lens mounts can be found here: http://en.wikipedia.org/wiki/Flange_focal_distance
As a rule of thumb, you should be able to mount a lens with a longer flange on a body with a shorter flange, but I'm sure there are exceptions.
Last edited by Halka; 12-06-2012 at 10:44 AM. Click to view previous post history.