Clinical studies

The best place for information about ongoing clinical studies in the USA, whether you are elegible and how to participate is at the National Institutes of Health (NIH) website, which has a whole section devoted to clinical trials called ClinicalTrials.gov . There are links to a lot of detailed information on clinical trials as well as details of the trials themselves. The trials database is searchable, and you don't need to preregister before using the site - all paid for by the US government.

For information on ongoing trials throughout the world (including USA) there is a good website called the Centrewatch clinical trials listing service. Again, there is a lot of useful information which you do not have to register or subscribe to for access. They claim to have details on 41 000 ongoing trials and you can even sign up to an Email service which will Email you when any suitable trails start up that you may want to participate in.
Equally useful is a listing of all the drugs most recently approved in the USA by the Federal and Drugs Administration (FDA)

The site at Oncolink provides some information about insurance coverage for participating in a clinical trial.

The list goes on - search with 'clinical trials' on the excellent search engine at www.google.com for many more links