Federal:
21 U.S.C. 801 et seq. (the CSA)
The Cole Memorandum (DOJ guidance to US Attorneys regarding enforcement of the federal marijuana ban)
BSA Expectations Regarding Marijuana-Related Businesses (FinCen guidance to banks regarding providing services to marijuana-related businesses)
Rohrabacher Farr Amendment (appropriations rider that bars the DOJ from spending appropriated funds to prevent the implementation of state medical marijuana laws)
United States v. McIntosh, 833 F.3d 1163 (9th Cir. 2016) (key case interpreting Rohrabacher-Farr) 

New York:
NY Compassionate Care Act (original enabling legislation)
NY Medical Use of Marihuana Program Regulations (implementing regulations)
NY State Medical Marijuana Program (program website)
NY State Bar Association, Opinion 1024, Counseling Clients in Illegal Conduct: Medical Marijuana Law