It's called Wall-Pops. You can find it at our local hardware store or I imagine online.
It's such an easy way to decorate a room. I wasn't even looking to do this but I saw it today and it was so cheap I had to try it.
Here's Arianna's wall before:
Here's her wall after I added the wall-pops:
Isn't it so cute!! It cost me: are you ready for this???
Better yet- they are completely re-positionable. You can peel them off and re-put them anywhere you want. I love these things. They have all kinds of designs and colors to pick from.
What a cheap, great way to re-do a room and in about 15 minutes!!