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) 
Sessions Memorandum on Marijuana Enforcement [January 4, 2018]

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
Assessment of the Potential Impact of Regulated Marijuana in New York State (New York State Department of Health, July 2018)
New York State Interagency Working Group to Study Possible Legalization
New York State Conducts 17 Regulated Marijuana Listening Sessions
New York State's Medical Marijuana Program: NYCRR Part 1004

NYSBA Articles of Interest
State Bar News Article - Cannabis Committee Created
State Bar News Article - Making Sense of NY Cannabis Law
NYSBA Press Release - NYSBA Creates New Committees to Examine Cannabis and Transportation Law
The Environmental Lawyer Article - Legal Pot Industry Bugged by Lack of Pesticide Guidance by Telisport W. Putsavage

Academic Blogs and Research Sites
Brookings Think-tank that conducts research on marijuana policy (among other topics)
Marijuana Law, Policy, and Authority. Law professor blog and textbook website covering broad range of developments in marijuana law. By Professor and Committee on Cannabis Law Academic Advisor Robert Mikos.
Marijuana Law, Policy & Reform. Law professor blog covering broad range of developments in marijuana law. By Professor Doug Berman.
National Conference of State Legislatures (NCSL). Compiles information on  state marijuana reforms.
RAND Drug Policy Research Center. Think-tank that conducts research on marijuana policy (among other topics).
Social Science Research Network (SSRN). Searchable database of social science research on marijuana law and policy (among many other topics).  

Bar Association Groups
Michigan State Bar Marijuana Law Section
National Cannabis Bar Association
Oregon State Bar Cannabis Section

News Sites
Cannabis Law Report. News site covering broad range of topics concerning marijuana, and especially marijuana law.
The Cannabist. News site started by Denver Post; covers broad range of topics concerning marijuana.
Cannifornian. News site started by several media outlets; covers broad range of topics concerning marijuana, with a particular focus on California.