I'd draw your attention to a study that was just put out by Michael Wolfson, former assistant chief statistician, noting that the government had promised to review tax expenditures benefiting those at the very high end of the income spectrum. The two that would leap out would be the special treatment of stock options and the amount of capital gains that is not subject to tax.
I think on the stock options we all know it's a little tricky in how you limit it without completely obliterating it for tech start-ups and so on. A massive amount of the stock options deduction benefits senior corporate executives who are compensated through options as opposed to regular salary. I think there's a significant amount of money to be made there.