I only know what I've done.
Cannabis (weed, marijuana) - makes you feel very mellow, but depends on the strain. Indica can make you very sleepy, while sativa makes you quite stimulated. Music sounds better, movies look better, and trains of thought seem to go on forever. A joint will leave you high for about two hours. Can make you vomit if you smoke too much.
Speed (amphetamine, base, whizz) - makes you very stimulated, chatty, hyperactive, extremely confident, and quite horny, but also makes it hard to get an erection. Depends on how much you take, but can last up to a few hours on one dose. Comedown from ordinary amphetamine isn't particularly pleasant.
Crystal meth (tina, glass) - same as speed but the comedown is horrific.
Cocaine (gak, coke) - basically exactly the same as speed, but marginally more intense and one dose only lasts half an hour.
Ketamine (special k) - it's an anaesthetic so it makes you feel as though there's some distance between body and brain, in small doses it just feels a little floaty or like you're in water. Anything physical feels like it takes a huge amount of effort and takes forever to do. Hallucinogenic in high doses, but I've never had that much. Lasts about half an hour.
Mephedrone (m-cat, meow) - like a cross between ecstasy and speed. Has the hyperactivity of speed, and some of the positive qualities of ecstasy but is much messier and more confused, a bit like being drunk. Lasts about two hours.
Ecstasy (pills, MDMA, molly, E) - by far the Ferrari of club drugs. Has the hyperactivity of speed, but also an indescribable feeling of connectedness that no other drug comes close to. You want to hug people, you want to talk about really deep subjects for hours on end, music sounds amazing, dancing feels amazing. Sex is beyond amazing, especially with someone you love. It's hard to verbalise how great it is. Unfortunately, the more you do it, the lesser the effects become and once it's gone, no amount of abstinence ever brings it back. Lasts about four hours.
MDA (Adam) - you may sometimes be sold this as E. It's chemically similar and has similar effects, but lacks the loved up quality that makes ecstasy so unique. It also comes with quite pleasant fractal hallucinations, but a much longer duration of up to eight hours.