The National Science Foundation funds several programs that provide research experiences for undergraduates. You can see a list of programs for 2016 and see whether any of these might be right for you.
Start exploring soon, since several of these have deadlines in early February, and a few in late January. Check carefully, since a very few of the links point to information that pertains to summer 2015; in that case, consider writing to these programs to see if there is a program for the upcoming summer. Be careful to check criteria for eligibility, or preferences that these programs have (e.g., people planning to graduate in 2017).