Summer Undergraduate Research Program. I'm pretty sure they allow anyone with an interest in either research or medicine to apply for it. Unfortunately, almost all of the programs had application deadlines of March 1st for this summer, but if you're a sophomore right now, it'd be perfect for you to apply next spring. Just go to
http://www.unmc.edu/dept/summerresearch/
There's a TON of different programs you can apply for, and there may also be some still open for application (just not the ones I applied for). The SURP at UNMC generally is 10 wks long (basically the whole summer) and they give you a stipend of $3k for your work. It works out really well if you have someone in Omaha, NE to stay with, then you get to bank most of your stipend!! (I'm staying with my aunt for free, so I basically get to keep all my money!)