2008 is shaping up to be the year that street art went truly mainstream in London. Currently, you can see Banksy at Selfridges, a half-mile tunnel of talent in Waterloo and, for the eagle-eyed, that subtle bit of wall painting at the Tate Modern. Street art is also getting big in the more literal sense. Here are just a few of the supersized pieces around town at the moment. At the top of the......