Erowid is a non-profit organization that provides information about many psychoactive plants and chemicals.
A useful index of various drugs and their effects.
Erowid’s comprehensive page on MDMA (Ecstacy):
EcstasyData.org was created to “collect, manage, review, and present laboratory pill testing results from a variety of organizations.”
Drugs-forum is an “information hub of high-standards and a platform where people can freely discuss recreational drugs in a mature, intelligent manner.”
Trip Project has a long history of providing useful drug and health information.
TripSit’s mission is to provide open discussion of harm reduction techniques and positive support. They promote the use of harm reduction tools such as test kits, and offer guidance and support with regards to harm reduction when using drugs.
TripSit also has a useful wiki:
DrugRehab.com provides information and answers for people fighting addiction.
The U.S. Department of Justice technical document specifying the standards for color test kits for the identification of drugs.
A substance chart where you can compare the color reactions for three tests (Marquis, Mandelin, Mecke). (63KB PDF)
Special thanks to Ekstasis for this chart.
For those interested in the major studies of drugs and drug policy, the Schaffer Library of Drug Policy contains a huge collection of documents.
Know of any other useful links? Please share them with us so we can publish them here.