Netherlands (near Amsterdam): Don't buy on the street, because you will get scammed. If you buy at parties you probably will get decent products, although I've never tried that. The best way is getting to know a dealer. This is not hard, in most outgoing young groups of friends at least 2-3 people will know someone or multiple people who sell drugs. Because we can have our drugs legally tested for purity quality is generally pretty good. Dealers that I've met were generally pretty nice. I don't think many people get robbed or whatever, unless of course you're being stupid and buying off random people in the street who ask if you want to buy cocaine.
Most popular drug (after weed probably) by far is MDMA. Pills are very good at the moment (very often 200mg+) and almost never contain any adulterants. They are cheap (so cheap that what you have in your wallet at any point will probably be enough to buy some pills). MDMA crystals are also pretty widely available. Among young people, XTC use is often accepted. I used to work at a bank inbound callcenter where most employees were between 20 and 35 and when I got to know them it turned out a large amount of them regularly used XTC. As XTC use here started in the 90's the 30-35 year olds also often had a LOT of XTC experience.
Speed (amphetamine) is also pretty widely available, but varies a bit more in quality. It's important to find a consistent dealer or get it tested. It is even cheaper (the change in your pocket will suffice for a gram). Meth is available but not considered desirable by most people and mainly used by speed addicts. I think most people don't even know that it's available here, although they know of its existence through the documentaries and news about the USA.
Mushrooms have been outlawed, but truffles are still legal.
Other popular drugs are GHB, coke (not very pure most of the time, crack is heavily taboo), ketamine (can be hard to find). LSD or 2c-b are also not too hard to get but a bit less popular. Heroin use is heavily frowned upon and only used in the heroin scene (mostly older addicts). It's probably easy to get if you know some users but I've never really been interested.
RC's are not very popular (probably because illegal drugs are easy to find), but I think at the moment 4-FA is rising in popularity. Mephedrone never really took off.
Police won't bother you too much in general, the policy is to prioritize catching dealers and if they catch you with certain (small and predetermined, for example 2 XTC pills or 1 gram of speed max) amounts of hard drugs they won't prosecute.
Drugs that are virtually unheard of here are PCP, "bath salts" (MDPV and related chemicals), prescription opiates (at least as far as I know, but maybe it's more prevalent in the closed heroin scene), DXM.