For me the big four would be:
* No 4/No 3 Powder heroin- It doesn't seem to exist here, I mean, people I know have seen it very occasionally (once every couple of years) and it's always fucking rubbish , you're better off using your money to buy morphine and making your own heroin (which is what we do). However it would be nice to be able to just dissolve some white powder in water, filter it and away you go instead of getting a pill and...[25-40 minutes of work later]...add a little citric and you've got yerself some heroin. Even No 3 heroin, which would involve using vinegar and 5 minutes effort, but it's still light years ahead of where we're at. And to think, until recently vials of pharmacutical diamorphine weren't that uncommon in the UK.
* Ketamine- It's the fucking ghost drug, everyone seems to like it, everyone seems to have taken it at some point or another, it's widely used in medicine/vet, it's widely produced/available in the developed third world (China, India, Brazil, etc) and yet...where is it? It;s a fucking mystery is what it is, I tells ya! Why is it that every other week fucking meth gets seized coming in from Asia, yet none of these people bother to think to buy some of that infinately-more-legal-and-available-than-meth drug?
* Amphetamine- You bloody europeans, with your excellent cheap drugs, superior research chemical vendors and massive availability of 'base putty'...you has it too easy! Makes you soft, soft and drug addled. But really, I don't enjoy meth, I don't enjoy stimulants a whole lot as a class, but I've got to admit that they can be damn useful. Need to get shit done and didn't sleep well, take a little speed. Getting your party on, but feeling kinda lethargic and lazy because you've been taking morphine and ketamine...take a little speed. Dexamphetamine pills aren't as versitile as amphetamine putty imo and amphetamine putty is actually amphetamine, unlike 'speed' which is just more fucking meth, this time cut 10:1. Most of the time when I need a little stimulant boost I'm reduced to methylphenidate. Actually being able to get excited about MDPV and ethylphenidate depresses me a little.
* PCP- I know that PCP is a drug of use (I won't say 'common', but you can get your hands on it) in central Europe (Germany/Poland/Austria seem to have it around), parts of Canada (particularly the French Speaking province of Quebec where it was/is sold as 'mescaline' and is fairly common in some scenes) and parts of the US of A, as far as I know it's more of a west coast thing with there being more around California and Texas. Why the fuck does it just not seem to travel anywhere, ever? You know what I mean, things like mescaline and dmt and pscilocin aren't available all the time, but if you buy acid regularly or keep in touch with folks who do for long enough chances are you will have the oppotunity to buy some. The same with ketamine, if you are in 'the scene' long enough you'll come across it, but it's not like you can just 'go get it'. But PCP isn't like that, you just never see it unless you live in very specific areas where PCP is a thing- or you are a chemist/have links to legitimate/clandestine chemists. And speaking of clandestine chemists, it's not THAT hard to make and the precursors, while controlled and watched, aren't that hard to come by, particularly if you think a little creatively and produce some structural analogue- yet you never really see it sort of 'appearing' places after some clever little wingnut did some small scale (but even just an ounce or two of PCP is a great deal of PCP) after scrounging together just enough of the required chemicals. I find this extremely dissapointing, I am fascinated by arylcyclohexaylamines and the dissociative experience- I hope that eventually I will be able to get my hands on some pcp. Not to mention all those tasty looking analogues...oh why must you tease me so!?