When I went to Amsterdam, I did this:

http://www.newamsterdamtours.com/

Its free and you donate what you think its worth to the guide at the end of the tour. I love listening to the guides talk about the history of the place, about how the city gives hard drugs to drug addicts (as long as they are functioning citizens) and so much more. Definitely worth it.

If you go nearer the start of your time there, you'll get more of an idea of what is out there to do / see for the rest of your trip.