The Dept. of Energy offers academic year and summer paid internships. Don't be misled by the "Energy" label--these laboratories conduct research in a vast array of scientific disciplines including life sciences, chemistry, physics, all sorts of engineering, environmental studies, and even social sciences.
Go to http://www.scied.science.doe.gov/scied/erulf/choose.html for a list of facilities and descriptions of the work conducted there.
Then, visit their website http://www.scied.science.doe.gov/scied/erulf/faq.html for application guidelines and other information.