I was just in Amsterdam in April. Great city. The Rijks museum just reopened after a 10 year renovation so definitely worth checking out. The smart shops will sell you real mushrooms and Molly if you ask but they aren't "on display". Otherwise just go to the clubs and get real ecstasy which is pretty common and really good.
The best club in Amsterdam is Trouw.
http://www.trouwamsterdam.nl/en/ We went to see Sven Vath spin and it was incredible. People will be a bit hesitate of you in the beginning since you are American but just give them some time and they'll warm up to you. They hate the British so as long as you don't act like a drunken reerun like the English do you should be fine.