Seeking Alpha have a good summary of each countries’ withholding tax rates for 2011.

Why should you be concern about withholding tax as a dividend income investor?

As a foreigner investing in other countries stock exchanges, unless your country has a tax treaty with that country, there is usually a tax on the dividend income or income in general.

The question is how much.

In this past article I explained my experiment to see how much withholding tax is levied on my Telefonica dividend purchase. The conclusion is that:

If you as an international investor invest in a international ADR listed both on the US stock exchange (as an ADR) and on its own stock exchange and you purchase the ADR, only the home country’s withholding tax is levied and not an additional 30% withholding tax.

A list of countries’ withholding tax rates

Top Foreign Stocks have a good break ...