Open websites, or those freely available on the web using a search engine like Google, are becoming increasingly valuable to researchers as more and more government, educational institutions, and foundations are providing information and data about their work online. While there is A LOT of great information out there, remember that anyone can put information on the open web, so evaluating the material to make sure it is credible becomes more difficult and important.
Many of the best sites to use are those from education (.edu), government (.gov), and private organizations & foundations (.org). To easily search for sites from these entities, use the "site:" search to limit your results.
Some example searches: "diabetes site:.gov"
methamphetamine addiction treatment site:gov
addict* famil* site:edu