I have a GINORMOUS shoot tomorrow. Something like 27 different lessons all in one shoot. Typically it's pretty easy to keep track of things, but I've never attempted so many lessons in a single day (at the most it has been 5-7). Even with 1 or 2 Camera set ups, this is a necessity:
The Movie Slate App- Turns you iPad into a Digital Movie Slate! So far I am loving it, highly customizable. We don't even really need it to sync cameras because most of the lessons are one camera shoots, but something tells me I will be using it more in the future. Slates are awesome for syncing up multiple cameras so you can jump around from one shot to the other in editing, it gives you a reference starting point and helps with organization. We are going to use it primarily to keep track of which lessons we are shooting. At $20 its a great deal compared to the professional slates.
It also works on the iPhone!
Movie Slate App