Two words, Tobin Taxes.
Essentially, any money crossing the border is taxed at some tiny amount (0.025% or so). The system was thought of by an economist named what else, Tobin.
It is estimated that around 300 billion (or so, I can't recall the figure right now, in the hundreds of billions) per year would be taxed in this form, and it would put a serious damper on offshore tax havens.
Think of it - 300 billion per year. For that money, you could feed and clothe and educate every person on this earth. And its not like you can make the arguement that business will leave; where are they going to go if the whole world implements this? The businesses affected by this would not be your Mom and Pop store, they don't transfer significant amounts of money acorss borders. The ones who would be made to pay are the huge multinationals, who are currently paying, as mikhael said, 0 taxes. And its not like they can afford it.
An anecdotale statistic, if you can call it that. According to some NSF guy in Deus Ex, in 1950 50% of all government taxes came from corporations. In 2000, that sum was 5%. Hehe, I'm inclined to believe it

:D