I first published a post about street art in Oslo back in October 2012: http://paulamdeangelis.blogspot.no/2012/10/street-art-in-oslo.html. I am always looking for more of it when I walk around the city, and every now and then I luck out. Like with these images--colorful and different. I don't know who the artists are, but they sure don't lack for imagination.
If you want to check out some really good street art sites on Facebook, try Street Art in the United States: https://www.facebook.com/streetartunitedstates and Street Art in Germany: https://www.facebook.com/StreetArtGermany.