For my Oly's the ones that came with them, aprox. 4cm wide, B&W
For my "new" RB I have to buy one yet, thinking of: www.optechusa.com for it.
For my SL 66 I don't use one, I have the grip and that works for me
For my Rolleiflex 2.8F I need to get a new one too: the old leather one broke in several places, kept the att. though
and a P2 with a neck-strap ?