I am gearing up for Crow Slaying '13 tomorrow and was trying to get an electronic call in the mix. Found the iHunt app on itunes and so far it looks pretty badass. You can create a playlist of calls to repeat, delay, etc.
Some of the animals featured:
crows coyotes geese cows bear etc...
Plug a set of speakers into the headphone jack and let the good times roll. $3.99