Quoted from wikipedia:
Street art is any art developed in public spaces — that is, “in the streets” — though the term usually refers to art of an illicit nature, as opposed to government sponsored initiatives. The term can include traditional graffiti artwork, stencil graffiti, sticker art, wheatpasting and street poster art, video projection, art intervention, guerrilla art, flash mobbing and street installations. Typically, the term Street Art or the more specific Post-Graffiti is used to distinguish contemporary public-space artwork from territorial graffiti, vandalism, and corporate art.
Subway Greeting: Shot taken in London, UK (2006); Originally uploaded by daveknapik
Tough Santa: pic taken in Montreal, Canada, 2008 (originally uploaded by Christian et Cie)
Sneaking Elfvis: part of a series of graffiti art found in the streets of Auckland, New Zealand, 2007 (originally uploaded by Robyn Gallagher)
Holiday Satire: a stenciled message taken in Norwich, UK, Dec. 2007 (originally uploaded by Simon_K)
Statement on Consumerism: taken in Jan. 2008, somewhere in Canada (originally uploaded by sin against nature)