The ones i use are:
Endomondo: walking/exercise/fitness tracking app.
Flipboard: great way to integrate your feeds/facebook in one place
Sun Surveyor: see where the sun is going to be, useful for photography
Waze: social satnav and traffic notifications.
WeatherPro: excellent weather app and very accurate 14 forecasts
TP forums: of course!
Sonic CD: Enhanced version of the Sega CD classic game. lots of fun.
MD.Emu: Sega Megadrive Emulator, again lots of fun.
HyperQuiz: General knowledge quiz, love this.
AngryBirds - all 4 games... great fun to play on a rainy sunday afternoon
LanSolCal/Widgets - a nice little app that gives you the sunrise, sunset, twilight, moon phases in a lovely widget and more detailed info in the app.
DOF Calculator: good for calculating dof for group shots etc on the go.
Google Drive: Nice integrated online storage, very useful for carrying around files.
And maybe the biggie i couldn't live without:
Swiftkey. If you do any amount of typing, you need this app. it's a replacement keyboard that learns how you write. it's scary because it starts to read your mind. Just updated to v3, even better.