The tax laws change on almost an annual basis but for 2012 dividends were taxed as short term capital gains (which was the same as income tax) unless they were qualified.
Qualified dividends were dividends distributed by US companies and which were held for at least two months during the 4 month period before the dividend was paid.
For 2013, dividends are considered as short term capital gains and attract the same tax that is applied for income.