Foursquare - Every time you go to the explore tab in the foursquare app, it gives you different examples of what you can search for.
Wunderlist - The desktop version has one form for both signup and login.
/via Denise Pires
Feather iOS App - The Twitter bird turns slowly green as you type and goes red when you get to the 140 character limit.
/via Anna PS
Path - If you forgot to add one of the three requirements while uploading a photo on Path for iPhone, the buttons bounce as you tap on Save.
OSX - Excellent integration of the MacApp Store into the OS for unknown file types.
/via Pete Wilkinson
Mac App Store - The progress bar of installing an app from the Mac App Store changes its dimension separate from the icon, when magnified in the dock.
Calculator App - When you rotate your iPod, the app uses the screen real-estate to add functions.
Twitter for iPad - Swiping your timeline to the right, removes the content layer. It’s visualized by a little animation behind the timeline.