Some of my often-used apps:

-Rowi (for Twitter)

-Wooter (woot.com app)

-YouTube

-Yelp

-TransitFinder and StopGoStopGo for Boston MBTA service alerts/schedules

-Skyview is a sorta-decent celestial constellation app

Games: -Shuriken Ninja, Angry Birds, geoDefense, Beards and Beaks, Plants vs. Zombies, Krashlander, Pandas vs. Ninjas (free Angry Birds clone)