The Facebook app is a major spy tool, it has access to your contacts, your location, etc. Too creepy, I deleted it. I can access FB via the browser, which works well enough.
For fun: DrumKit, Virtuoso, MyGuitar, Baby Scratch, and MoBeat are all free instrument/ DJing apps. Other fun stuff: Rubik's Cube, iGunLight, Spawn, Jet Ball.
I still love CNN and the NYTimes app, both super awesome. Same goes for HuffPo. CNN has been a gem, you get free notifications.
I also digg the various barcode apps, you can check where your food really comes from, very enlightening.
Hipstamatic and Tiltshift are both fun photo tools.
LastFM is very useful, too. Not to forget those apps that monitor traffic jams and radar controls in your area. Wikihood is my latest nerd obsession...
All of these are free.