www.nyanit.com
Eventually the nyancats fill up your whole screen and you can't see a thing. I can't see what I'm typing right now.
(http://i1212.photobucket.com/albums/cc451/Hamilah/Nyanit_zps3295e534.png)
Can be done for any website! Enjoy the nyan cats filling up your screen and blinding you with their rainbows.
I'm surprised how I typed this all with the nyan cats completely blocking my sight and with almost no mistakes
EDIT: Oh, you can click away the nyan cats XD
I can't even log in with its soooooooooo annoying with the music
THE MUSIC IS ANNOYING (http://oi39.tinypic.com/e5k5s7.jpg)