The possibilities for pro-weed commercials are endless.

A black guy in a jail cell: "President Bush smoked marijuana. President Clinton smoked marijuana. I smoked marijuana. Why am I the only one in jail?"

It couldn't hurt to throw some statistics in...

"You're told that one joint is equal to four cigarettes worth of carcinogens.Tobacco smoking causes an estimated 5 million deaths every year. In the history of mankind, there has not been one death that has been conclusively linked to marijuana smoking. Harmless? Pretty much."

EDIT: That reminds me. You can find some pro-weed parodies of the "Harmless?" commercials on this guy's web site: http://www.whatthefawk.com/index.php?a=flash