A pretty awesome video of graffiti artists spraying up a metro train.  Unfortunately, little is known about this group, and the Youtube video didn't offer an clues as to where they are or anything else about them.  This is considered street art because it shows how this bland train is transformed into work of art.

An interesting video on the graffiti and graffiti artists around Bristol and the views on tagging.  Part one of four. 

The evolution of man according to Blu.  His work reminds me of Shel Silverstein, but that's just me.  Again, little is known about the artist Blu.  His website provides samples of his artwork and links to other graffiti artists websites, but doesn't say much about him.  There is no page on Wikipedia about him (yet), and all of this proves he's the real deal.  Anonymity is the graffiti artists best friend, and Blu uses it to the fullest.