The bar code scanner. I just scan a product in a store to see the price as well as comparative where I can get cheaper. I love it. both for iOS & Android. There is photo recognition as well. Like if there is no bar code. Take a picture and it will try to match the actual. Mostly works.
The ustream app. You can send live video / audio and share it via a url. If you have good bandwidth , i mean 3G and up., dozen of people can watch it live. Excellent app both for iOS and Android