It's a really photogenic city and you kind of can't miss. Shinjuku is the traditional district for interesting street fauna; Akihabara is worthwhile as well, though the back alleys of little electronics shops apparently have *much* less character than they used to. (I think you're not supposed to photograph the store greeters in the French maid outfits.) The bay front is quite scenic in an urban-bay way; the best views might be from Odaiba. But basically, just get out and wander. Get off the main streets and into the residential districts and the city changes very, very quickly---it has a reputation as a bright-neon never-sleeps megalopolis, but you wouldn't know it even from some of the places within a couple of blocks of the major thoroughfares.
As a random sidelight, I really recommend the Ramen Museum in Shin-Yokohama! It's not a big photo attraction, but it's well worth while.