There's a good list of 16 photography apps for the iPad on photography talk.com. I like many of these selections. Serious shooters should consider the upgrade to Filterstorm Pro that has better organization features and Raw processing, compared to the basic app included on the list.
Another app on the list, PhotoSync is really useful for moving pictures between devices, even in the age of Photo Stream.
One important omission, in my opinion, is Minimal Folio that is a terrific tool for organizing and displaying a portfolio of your best work.
The bottom line is, there are many good applications for photographers available these days. Peruse this list and see if something sings to you.
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