Various clinics around the county are running either government or industry sponsored that is in need of participates. Most of the time you will either receive compensation, free or reduced-cost pharmaceuticals and reduced-cost protocol/treatments. Some of these trials are for new drug therapies in research and those recently approved by the FDA. You can subscribe (for free) to be notified of trials in your chosen area etc.
One suggestion would be to talk to your RE also. Sometimes your clinic will be needing participants for an upcoming study, so find out through them how to be added to the list.
