I've got three. SyncSlate, Marker Slate, and Movie*Slate. Of the three, I mainly use Movie*Slate, though the others are quite a bit cheaper. I rather like that Movie*Slate stores all the shot data for later use, and also access the GPS/WIFI to log your location.
That said, the others may do some or all of this, but like I said, I haven't really used the others.