You guessed right if you said two, the Rothchilds and Rockefellers but of course that is a no-brainer. This question and answer from WikiAnswers is from a few years back and it is interesting to note that the Bildeburger group is mentioned, however alleged it claims.
---------------------------------------

A: Who was the world's first trillionaire? The answer is no one.....yet! Bill Gates reached the apex of his net worth in 1999 topping the $100 billion mark, but has since slipped to about $50 billion. In 1999, calculating the growth rate of his holdings he was expected to reach one trillion dollars in 2004 or 2005. Obviously it did not happen, but he is still by far the closest. Here are some facts about a trillion dollars: * If you were to spend a million dollars a day it would take you 2,737.8 years to spend it assuming you made no interest. * At 5% interest you'd earn about $136,986,301.00 per day, $5,707,762.00 per hour, $95,129.00 per minute or $1,585 per second. * According to Forbes in 2005 the 691 billionaires in the world are worth $2.2 trillion combined. * On October 18 2005 the American National Debt surpassed $8 trillion.

$9,415,320,760,775
US National Debt

There are at least two banking familied that are credited with being multi-trillionaires. The exceptionally wealthy Rothschilds are estimated to be worth between $400 trillion dollars. There are 300 families in the alleged 'Bildeburger' group and their banking methods and investments in weapons and oil are worldwide. Even families such as the Rockefellers are estimated to have between $6-£10 trillion, so there are definitely trillionaires in the world; we just don't get to hear about it properly. Just search for rothschilds wealth in Google and you will see the hundreds of billions that these families invest DAILY.

http://wiki.answers.com/Q/How_many_trillionaires_are_there_in_the_w...