Beijing - China -->
K-分 (Ketamine, literally translates to K-Powder)
冰 (Crystal Methamphetamine, literally translates to Ice)
摇头药 (Ecstasy, literally translates to Shake-Head-Medicine)
大麻 (Marijuana)
Those are the most popular, but in total, I've seen -->
Heroin, Cocaine, Ecstasy, Crystal Methamphetamine, Hashish/Marijuana, Ketamine, Psilocybin Mushrooms (season dependent) and extremely rarely --> LSD, MDPV-and-other-RCs, Prescription pills and Medical-grade-or-close Marijuana.
The drugs various drugs come from-->
Heroin: It comes from the Golden Crescent (Afghanistan, Iran and Pakistan) and from the Golden Triangle (Burma, Vietnam, Laos and Thailand).
Cocaine: It comes from S. America, with W. Africa as a trans-shipment point.
Ecstasy: It comes from domestic producers in S. China (allegedly with Hong Kong chemist know-how overseeing labs)
Crystal Methamphetamine: See Ecstasy. China has extremely cheap and high grade Crystal Methamphetamine (as precursors and other necessary ingredients are readily available with lax government control).
Hashish/Marijuana: Domestically it mostly comes from Yun-Nan/Xin-Jiang provinces. Increasingly though, the better stuff is coming from indoor operations on the outskirts of cities like Beijing, Shanghai etc. Rarely, a low quantity of great marijuana will come from Canada/US/S. America.
Ketamine: Huge industrial-scale production all over China from legitimate manufacturers, that gets diverted for illicit use.
Psilocybin Mushrooms: It comes from Thailand and generally only during Summer months.
RCs/LSD/Prescription Pills/Amazing Marijuana: Anywhere in the world - generally one-offs from travelers that smuggle low quantities in.
I hope everyone enjoyed learning about the Beijing drugs!
Edit: Added
BOLD!