B&H for overall "you want, we got"... Plus they're nice people to deal with. Not the cheapest, but I'd rank them a strong 96 points on the CamelNast Whine and Widget Conesuers Guide.
Ranking immediately below them (only because their inventory isn't *quite* as extensive, but great nonetheless) for Nikon goodies is Abes of Maine. Found them quite by accident via Amazon... I've had nothing but excellent luck with them. The upside is their prices. They *do* try to promo packages, if you don't want them say so but occasionally the *do* have some good "combo" deals...