One thing you should do, and it took me until my seventh trip there to do, go on the open top tour around the town, yes I know it is the most touristy thing you can actually do but it is worth it as you see some of the more off the track places
the eastern suburbs are worth a look, there is also Neu Camp stadium, really good architectural shots, the olympic stadium is worth a visit, again great architectural shots, the central bull ring was being worked on the last time we were there so no idea if it is still worth taking photographs or has been converted into a shopping centre now
another good area is Bario Chino, the opposite side of Las Ramblas from the central Cathedral, less development there and a large North African population
Oh, another good recce is the cable car trip from the harbour, great overview of the city and once at the top of the hill there are really good views over the city
If I can think of any more I will post them
one of the best things about Barcelona are the people though, some great opportunities which I always missed as I used to be too shy to take pictures of people, this was taken from the open top bus