NYT has a good piece on Saudi support for Hamas.
At least 50 percent of Hamas’s current operating budget of about $10 million a year comes from people in Saudi Arabia, according to estimates by American law enforcement officials, American diplomats in the Middle East and Israeli officials. After the attacks on Sept. 11, 2001, the Saudi portion of Hamas financing grew larger as donations from the United States, Europe and other Persian Gulf countries dried up, American officials and analysts said.
The estimated donations coming from Saudi Arabia–about $5 million a year–are a significant sum for Hamas but a very small portion of the hundreds of millions of dollars that flow into Saudi charities each year, officials said. Nearly all the donations are given in cash, making it extremely difficult for Saudi and American authorities to track the money.