in addition to free clinics and giving/selling blood (both of which can make you waste an entire afternoon waiting...)
there are clinics that do studies (back pain, headache, allergy etc) they advertise on the tv and radio, there is also a Black Book with all the clinics that routinely have studies, buy that online for, like 19.95
these places do medicinal trials, and as such, take your blood and make you pee in a cup anywhere from weekly to monthly to every 6 months... they Will tell you if you have Anything and you get $20, $40 or more each visit for participating in the study.
Stay Clean and get movie money, prety cool, huh?
Nicole