scri.ch - The 404 is a regular scri.ch drawing (you can draw on it and save it as a new drawing).
iOS 6 - Keyboard detects specifics of language and displays correct diacritics depending on the part of a word.
GitHub - The cat illustration on the status page changes expression based on how the site is operating.
Twitter - If you follow a “Tweet” link when not signed in, the Twitter dialog window allows you to sign in & Tweet in one action.
/via Rich Dooley
Google maps - The android application ad in the left panel displays the map that you are currently viewing.
/via Ahmed H. Alley
Facebook Help Center - The search box contains a personalized message when you’re logged in.
/via Jimmy Oliger
Tumblr - When someone you follow re-blogs someone you don’t, a mini follow button appears inline with the post.
/via Brian Jacobs