Par(king) Day 2008 is September 19th:
PARK(ing) Day is a one-day, global event centered in San Francisco where artists, activists, and citizens collaborate to temporarily transform metered parking spots into “PARK(ing)” spaces: temporary public parks.
The image above is from Phillips Garden, a Minneapolis participant in Park(ing) Day 2007. Park(ing) Day was founded by REBAR, a San Francisco group, and has since taken off to cities around the world. Here's the first Park(ing) Day installation from November 2005.
Via Greater Greater Washington.