My first two that come to mind:

Favorite animal Calls - I have a Motorola t505 stereo bluetooth speakerphone that connects to my droid. While using this app and using distressed rabbit it is very loud. I'm thinking of using this for yote hunting without buying an expensive game call.

Google Earth- From your spot in the woods hit "my location" and have it show you the overhead picture of the land your hunting. Then click lookaround button and look for miles! Awesome!

I'm interested to see everyone elses.