Am soon going to be buying one and have no knowledge about them at all. Does anyone have any advice on which is the best to buy - will be photographing interiors of old buildings with a 20 - 200 lens (also looking into pano photography - see other post).

My friend had an SB800 but I'm also looking for some 'flash for dummies' type info.

Thanks

SB900 is the Nikon flash for "dummies". Very simple to use, the only one I've ever been able to figure out. You can use it "off camera" and the camera flash will fire the off camera flash. As a matter of fact you can set the on camera flash to not fire and have the off camera fire. You can set up several SB900's around and have the camera fire them all even if it can't see the flashes. No cables, no trigger mechanisms required. I bought mine from B&H Photo, I think for $400US each. This is of course the newest Nikon flash. The flash will also zoom, I think 17 to 200mm.
Just checked looks like they have gone up in price...I paid $812US for 2 of them in December, had to get them in time for a tax write-off.