Seriously, just volunteer at the hospital or a walk-in clinic. I love it, and I get great volunteer hours. Remember, only do something if you actually want it, no point in wasting a summer toiling away for no reason. These are precious summers before we all grow up, and move out!
If you work at a walk-in clinic, expect mainly clerical duties. If you're a Spanish speaker, it's very beneficial, at least it's helped me with our demographics. I've done like every job except fill prescriptions and see patients. I'm 16, and I'm considerably younger than all other student volunteers (think like 5+ years). Act very mature if you are reasonably young like me, otherwise they won't exactly like you. I have shown true interest in helping my community by being a translator, file-researcher, verifying bills, ckecking people in, getting large groups of volunteers get situated/started on work, scrubbed bathrooms, cleaned windows, take out trash, audit files, organize storage facilities, and ridding clinic of old/useless meds or monitors. It's a fairly tough job, but I work harder (while enjoying it, we're like a family

) than like 90% of the volunteers (who are older and looking for careers in medicine) so my co-workers know that I'm fully committed.
If you don't like the sound of this, you can always contact a professor at a local state uni to conduct research on a topic you actually like. I don't have that luxury, so I decided to help the community a bit :P.