Mailmonkey
Bluelighter
ketamine
ketamine
yeah, got to be good speed really innit.
The only problem with that is the potential to become very distracted by any good looking females in the vicinity.....
Hmmmm, suppose so, maybe mdpv or meph then
Seriously though, if you're not experienced with these things you'd be a dick to ingest them in the hope that they'll magic you through your exams. You might as well just do a bit more work and try to eat and sleep well in the week leading up to the exam.
If you're not going to go down the drugs route and if allowed to eat during the exam I've always found that a humble apple is absolutely excellent for rapidly clearing, energising and re-focusing a tired or fogged brain...