There's a few clapper board apps out there already for the iPhone and iPad, but several people reckon that Movie★Slate is the best because it has a number of features not available in others, including the ability to log yours shots.
Version 2.0 is out now and it features:
- HD-Optimized for iPad
- Timecode Sync from Camera LTC (optional in-app purchase)
- 6 optional data fields on main slate
iTunes: Movie★Slate (Clapperboard & Shot Log) - PureBlend Software