Shutter Snitch if you want to shoot wireless from camera to iPad (or iPhone)
You'll be sorry you asked
Photogene
Longtime
DSLR Toolkit
Photo fx ultra
Diptic
DSLRemote
Lighttrac
Photostudio HD
PS Express
Photosync
TPE (The Photographer's Ephemeris)
Filterstorm
.... and many many more.
DPReview yesterday: Tool or Toy? The Apple iPad 2 for Photographers