Many big universities, companies and government agencies all offer a chance to work in their labs for the summer. Typically you will receive a modest amount of money, enough for board and lodging and some fun, and get a chance to work in a big research lab. This can not only get you experience, it will also give you a foot in the door if you want to work/study in that lab after graduation.

Most require you to commit for several weeks, usually 6 or more, so it will eat up most of your summer. The working hours will be 40 hour plus in most cases. University jobs may also give you time for seminars and other activities.