Probably on your way on your trip already, but when living in The Hague I used to like going to Herman Buitelaar's shop in Gouda.
http://buitelaar.nl His english is great. I did walk to his new store from the Gouda train station last time I was there. (I love walking)
SSN in Rotterdam – again, moved since I lived there, but easily walkable from a Rotterdam station (http://stoomstichting.nl)
Railway museum in Utrecht. Army museum in Leiden. There's like 400 museums in The Netherlands, IIRC.
(googled the army museum – it's closing Jan 2013 – http://www.armymuseum.nl/get?site=legermuseum.en)
Enjoy your trip; when living there, I found the Dutch to be an incredibly nice bunch of people.
Another JohnS