Sto-Fen Omni-Bounce for the Nikon SB-900 Flash
The Omni-Bounce creates a Diffused Bare Bulb Effect. Giving even coverage across the entire frame, with lenses from 15mm to 200mm in the 35mm format. (And equal in other formats as well.)  The Omni-Bounce is easy to use and goes onto and off of your flash in seconds with custom fitting, except UNI, and No Velcro.  Designed for years of service with out the bulk of some other Diffusers, it is small enough to fit easily into your gadget bag or pocket.