Amazon.com : PhotoTrust 8"×8" (20cmX20cm) Universal Collapsible Round Studio Softbox Flash Diffuser for On Camera or Off Camera Flash Gun Compatible with Nikon SB-500 SB-600 SB-700 SB-800 SB-900 SB-910 Canon Speed :
The Nikon Creative Lighting System: Using the SB-600, SB-800, SB-900, and R1C1 Flashes: Hagen, Mike: 9781933952413: Amazon.com: Books
Amazon.com : The Flash X-Tender (Better Beamer) FX-4 Flash Output Booster for the Nikon SB-600 and SB-800 Flashes with Lenses 300mm : Camera Flashes : Electronics