Modafinil - obviously, the first on the list. This one, I would consider to be the most useful one of all nootropics that I tried and it's a crying shame that in the place where I live it is only prescribed to treat narcolepsy (and only if you can prove that it actually affects your quality of life). It's not strictly illegal though either, you can get it from abroad or just use adrafinil which is 100% legal.
I find it to be invaluable in situations where I need to wake up very early and engage in mentally exhausting activities for the rest of the day. I'm into motorsports and here is where it absolutely shines. I use armodafinil because the effect lasts as long as 8 to 10 hours, as opposed to modafinil's 5-7 hours.
The first hour after it "kicks in" is a bit intense (elevated heart beat, strong muscle tension), but for the rest of the day I can stay "on". Very much "on". I hear jet fighter pilots use it - I can totally see why. On empty stomach, modafinil starts working after about 10-15 minutes, armodafinil after about 30.
Another thing is, if I'm feeling hungry and I'm on an *afinil, I absolutely have to eat, even more than I usually do - otherwise it makes me miserable. Recreational value of *afinils IMO, questionable. Tolerance - no idea, I don't use it regularly.
Background: I'm middle-aged. Not suffering from anxiety or any other disorders, not to my knowledge. Blood pressure slightly lower than normal. No known conditions, no allergies, not taking any prescription medications. I've tried a wide range of nootropics and other substances throughout my lifetime.
My conclusion on nootropics overall: I would divide them into three categories - the ones that do nothing, the ones that do something noticeable quickly with possible negative aftereffects (this is what nootropics are about - treat them as drugs, benefit today, pay back tomorrow), and the stuff that's meant to down/up-regulate something long term. If you're taking something in that third category and unless you are a psychiatrist/neuroscientist, you don't know what you're doing. Don't. Messing with your neurotransmitters is extremely dangerous.