iMotionHD: This runs very smoothly to make either stop motion or time lapse movies.
Chess.com: We started an informal chess club and we are running it through this website. Also has iOS and android apps. Syncs great.
The Wider Image: Reuters story app using images. Good journalism.
DragonBox: Super cool app to teach algebra, but without doing "algebra". My 4 year old and 6 year old love app, as does my wife.
Haiku Deck: Presentation app that sets up your images really cool. Uses CC images.