Fred99:
I wouldn't "ban" plastic bags - but tax the crap out of them to the point that they're more expensive than biodegradable alternatives.
I think taxing the crap out of them is the wrong approach... what's needed is to do some calculation of the lifetime cost of a plastic bag (including disposal and/or recycling), and then tax them so they cost that much. Otherwise you'll be using biodegradable alternatives which use more resources and/or do more environmental damage (trees cut down for paper bags, energy use and environmental damage in processing the wood to paper, transportation) than what they replace.