With Photo Folder you can tag photos and sort them into folders. Works pretty well and if you have a lot of photos to sort through then the Photo Folders app could be just the job. You can rate them or make the favourites and tagging it nice and easy - puts the tags into the EXIF metadata. Then it also has the boolean searches than can be combined with the other sorting features so that you can drill down to the exact photo you want to use.
