Using panoramic Street View technologies, Google is assembling an awesome collection of high-resolution images capturing over 100 works in 5,000 interactive photographs to date, including many famous pieces from all over the globe (include now-destroyed paintings and tags).
Street artwork is often ephemeral, sometimes disappearing within a day of its creation, making this endeavor an ambitious attempt to document an art form frequently subject to being painted over by unhappy building owners or paid city workers. Art captured and presented here ranges from whole-wall exterior murals to floor-to-ceiling interior works, complete with online critiques, commentary and supplemental imagery.
The 5Pointz murals, for instance, were lost despite community protests, first painted over (presumably to lesson the blow of what was to come next) before the building they were on was destroyed entirely.
All of this is part of a larger endeavor, the Google Cultural Institute, which provides access to famous art and architectural interiors from around the world. The street artwork subsection lets you sort by artist or artwork, collection or location.