I wrote a post last year about volunteering to be a test subject for clinical research trials. Now CNN has an article on their website called Do you want to be a guinea pig (I think they left out the "Hey Buddy" part at the beginning), highlighting the increasing need for test subjects in clinical trials.
There are positives and negatives to participating in clinical trials. The biggest positives, in my mind, are that you generally get your medications and doctor's office visit paid for as part of the trial, and that you are helping to advance our knowledge of science and our ability to treat various medical conditions. Oh, and sometimes they actually give you money, too.
There are risks and drawbacks as well. For starters, if it's a blinded study (and they usually are), you don't know whether you're actually getting the test medication or a placebo. My local clinic sent me an offer to participate in a study of cholesterol medication, but it would have required that I stop taking the cholesterol medication I'm currently on, and only having a 50/50 chance of getting the study medication. That would have meant a 50 percent chance of not taking any cholesterol medication at all. Thanks, but no thanks. I'm more than willing to participate in the studies that are looking for "healthy volunteers" because those studies—usually earlier in the process—are designed to help figure out what tolerable, safe levels of the medication are. Basically, they're designed to compare any symptoms patients may get while taking various dosages of the medication to symptoms people who are taking the placebo get.
The CNN report has some tips you should ask before volunteering for any trials, so it's a good resource to take a look at if you've considered volunteering for any trials, maybe as a way to make a little extra cash in these tight times.