Mark Kleiman has a decent proposal:
Today’s laws criminalize millions of otherwise law-abiding individuals and create a multi-billion-dollar illicit market. Commercializtion would give the marketing geniuses who have done such a fine job persuading children to smoke tobacco, drink alcohol, and supersize themselves with junk food the opportunity to show what they could do with marijuana. Neither choice appeals to me.
My proposed law: It would be illegal to sell cannabis or to exchange it for anything of value, but not to grow it, possess it, use it, or give it away. I don’t imagine that the law would effectively prevent sales, any more than anti-gambling laws suppress private poker games. The goal would be to prevent marketing.
Read the whole thing.