The town of Delfft in Holland is a classic Dutch town, with canals windmills and a tower on the square you can climb for a great view.
If you're into WW II history, the "Bridge Too Far" has a nice museum and cemetary. It is not too far from A-dam by train. As a matter of fact, it seems like EVERYWHERE is not too far by train.
Check out my travelogue on Holland for more ideas, or to see what I did in my quickie trip over there...