Darrel West, a scholar at the respected Democrat-leaning think-tank The Brookings Institution, has recently compiled a ranking of the 19 most politically influential billionaires in the United States. (I'm not quite sure why he chose the top 19, rather than say the top 20.) Using a combination of the information given in West's original article, the pertinent individuals' Wikipedia and Forbes pages, as well as Google searches, I have identified the political views of each individual on the list.
Interestingly, nearly as many lean left as lean right. Now of course, it seems rather unlikely that any of the left-leaning billionaires are dyed-in-the-wool, sickle wielding, raise-the-red-flag communists; here we are presumably talking about the centre-left. Nevertheless, it is noteworthy that well-to-do activists with a left-of-centre disposition are over-represented at the top of West's ranking. In terms of absolute fractions, 47% lean right and 32% lean left. But if each person is weighted by the inverse of his rank (i.e., the Koch brothers get '19'), then 42% lean right, while 44% lean left.