My most used apps:

Google Music - copied about 15,000 songs from my collection out there and listen to music from my phone when I get a wirless connection.

Dropbox - I use this to share files and store files "in the cloud" so I always have access to them from any computer or my phones.

LED Flashlight App - There are several out there, turns your phones camera flash in to a flashlight. Very handy.

Skype App - I use this to communicate with friends in other countries.

Gmail App - Use this to access my Gmail account.

Compass - A pretty cool compass app.

Amazon - Used to buy stuff on my Amazon account.

Join.me - I use this so I can see other peoples computers when I am walking them through how to fix something.