Living in Germany since last January, I've had the chance to travel to several different areas in Europe and documents the sights.
I've read that Paris, London and Berlin are among the cities with the best street art. Though I suspect you need some time to explore and find the good stuff : ) If you have traveled and Europe and have some recommendations - let me know! Not all that I've listed here qualifies as "street art", but I thought it was cool. Here is a compilation of what I've seen so far during my travels....
Every street corner reveals little works of art.
I only had one day to explore London, so didnt't get to venture out of the more touristy areas.
HEIDELBERG AREA, GERMANY
Most of the murals are graffiti style, but you can find a little surprise one in a while (ok, the chalk drawings are a more literal interpretation of "street art".)
I was surprised at how much mural work there was in Genoa, Italy - many of these garage doors are painted with a mural. This is a beautiful city!
Unfortunately I didn't get to see much street art in Berlin, but maybe I wasn't in the right areas. Most of what you see is in East Side Gallery, which is one of the last remaining parts of the Berlin Wall. Though not officially "art", the photos of the cement blocks are part of the Holocaust Memorial that you walk through.
It's not "street art" but I did find many crucifixes along the bike paths through the vineyards.
BOLZANO, ITALY (along the Alta Via 1 trail)
This was the most surprising find. Along the rugged trails in the Dolomites, someone took the time to paint this frog rock. Maybe "trail art" is a more accurate term.