For ma nikon. Probably getting the SB-900, but I'm heavily looking at the 600. Is the 900 worth the extra money? What accessories do you recommend? It will be used as an on-camera flash for now (because my new lenses block the built-in flash), so I'll probably be getting a diffusor, some gels, and a shit-ton of rechargeable batteries.
Anything else I am forgetting that will come in handy?