not sure whether to put this in games an humor, or in here... didn't put it in games and humor because it's not a game and it's not humorous... it's just kinda neat.
http://gprime.net/video/pentricks.php
and
http://gprime.net/images/sidewalkchalkguy/
http://gprime.net/video/pentricks.php
and
http://gprime.net/images/sidewalkchalkguy/