Blog

First Time User Experiences is a showcase of new user experiences and onboarding flows, created by Krystal Higgins. See also Higgins' article on First time user experiences in mobile apps.

Via Leon

http://firsttimeux.tumblr.com/

Use Your Interface (UYI) is a showcase of interface and interaction transition design curated by Josh Davey.

http://useyourinterface.com/

This is a collection of videos of UI animations (mostly Apple) curated by @gardaud.

http://ui-animations.tumblr.com/