There's also Photosmith, if you're already using Lightroom:
"The photographer’s workflow just became easier. There’s no need to haul a computer into the field when an iPad with Photosmith  will do everything you need. There’s no duplicated effort in organizing  and tagging pictures, and it’s all done using a simple interface.
Now photographers can take their pictures in the field, download them to the iPad, and use Photosmith to review their images, add to custom collections, filter by certain criteria, assign metadata, and filter by that data. Photosmith  also fills a critical gap in the photographer’s current mobile  workflow- allowing full 1:1 zoom of even 21 megapixel RAW images.
Most importantly, all this data can be synchronized with Adobe’s  Lightroom. Instead of duplicating efforts or trying to import through  iTunes, Photosmith syncs directly to Lightroom on Windows or Mac using the Photosmith  Lightroom Plugin. All photos (RAW or JPG) and all metadata is  transferred over wirelessly. In addition, photos can be sent to  Facebook, Flickr, Dropbox, or email; and when supported, all keywords  and captions are sent as well."
I can't give you the link b/c I don't have enough posts, but do a search....