Nikon SB-R200 Speedlight Versus Nikon SB-600 Speedlight

If I can turn back the clock, I would seriously consider the Nikon SB-R200 instead of the SB-400 as my first flash. For $40 more, here's the reasons why:

Strengths

• Small and equally lightweight
• Its wireless and can be commanded directly from the Nikon D90
• Get it to sit on a table/floor or clamped onto a nearby stand/rack for flash operation AS-20
  
• Comes with colored filter sets SJ-R200
• Diffuser-friendly with SW-12
• Interoperable with Nikon SB-600/900
• Auto FP High-speed sync capable with Nikon D90
• FV Lock ready with i-TTL Nikon CLS capability

Weaknesses

• Cannot be mounted on Nikon D90 hot shoe, must be handheld or placed on the floor/clipped
• 50% lesser flash power over Nikon SB-400 (similar to built-in flash strength)
• White balance auto adjustment prompt to Nikon D90
• Uses less common battery type - CR123 versus AA

Nikon SB-600 has all the above advantages and a $100 dearer price tag than the Nikon SB-R200 but you get more power and WB auto adjustment in a heavier weight combo too.