Is there a 3rd party app to organize photos in camera roll?

No. Not possible with the current SDK, at least not with public frameworks. You can suggest Apple add that capability here:

http://www.apple.com/feedback/iphone.html

...but as a workaround, there are apps thatt allow you to copy photos from the camera roll, import them to the 3rd party app and organize them any way you like. You would view them with the 3rd party app and not the standard photo app on the device.

I wouldn't recommend wasting any money on an app. If you have a Mac with iPhoto then it should be pretty easy, but if you have a PC, I would recommend creating a folder (Doesn't matter what you name it or where it is) and going to the Photos tab when you're syncing and selecting that folder. Then you'll have to go to "*My Computer*" and drag and drop the photos to that folder you created. Then you can create sub-folders and and organize all your photos. A problem is that your iPhone can only read one level of sub-folders, but that shouldn't affect this task. I hope this helps! If you still can't figure it out, then try going to an *Apple Store* and ask a "Genius" for help.