DSLR Filmmaker Toolkit is a new app for iOS devices that combines a number of handy tools for, you guessed it, DSLR filmmakers. Current features include an electronic slate, shot log, depth-of-field calculator, level (for dolly/slider shots), daylight calculator, director's viewfinder and more. It's priced at $7.99 and available now through iTunes. I can't test it myself as I'm on Android, but here's a look at the app in action:
Video is no longer available: www.youtube.com/watch?v=MaZvSly3iSk
For an in-depth review of the app (which, keep in mind, is only $8), see a very helpful comment below from Darius.
Link: DSLR Toolkit