Serious sanctions would go a long way. We did it with South Africa. Then again, we're playing tiddlywinks with China so I shouldn't expect much to be done about Zimbabwe. Anyway, there's a reason why I don't talk much about these issues anymore on FR and I've been reminded why.
Sanctions are over-credited with South Africa's conversion away from apartheid. It wasn't the sanctions themselves, but the worldwide debate that they generated and the heat on SA. It became a huge cause and forced the westernized white minority to take a hard look at their country. Mugabe's reaction to sanctions will be similar to Saddam's: Hunker down, make the little people suffer. If they complain, kill them. If they complain more, blame the US.
And maybe SA isn't the best example of a success story.