This is an easy one for me: Epitalon. It's starting to get a little notice now, but for people like myself who have a terrible time getting to sleep because they can't turn their brain off, Epitalon was an absolute game changer. It literally worked the first night I dosed. Ran it for 13 days and nothing has changed. Come 10pm I could fall asleep standing up. Not sure if that's a good thing, but my sleep has done a 180. I'll run it again if I ever revert back to my old ways.
Silver medal goes to: Adamax. I work a stressful day job and this thing just keeps me focused all day long so 8 hours feels like 2 hours.
Haven't tried yet, but can't wait to start: Vilon and Vesugen. Heard great things.