Shazam - Listens to music playing and determines Artist, Album, and Title of song.
Tweetdeck & Facebook - Social Networking
myWireless - ATT application for account management (# of minutes used, Data used, ect...)
UrbanSpoon & Yelp - Finding awesome local restaurants no matter where you're at.
Kindle App - Instant access to any books you've downloaded to your Amazon Kindle.
Oakley Surf Report - Worldwide surf conditions. (Don't get to use this nearly as much as I'd like
)
The absolute most used 3rd party application on my phone is "Sound Level." Over the years I've experienced a little noise induced hearing loss and a moderate level of Tinnitus. (Caused by loud vehicles, high powered stereos, and guns.) Due to that I'm very sensitive to insuring I'm within safe dB levels. Any time I'm in a situation where I'm not sure of the sound level, I break out the phone to insure it's safe.