No need to detour via Amsterdam CS to get to Haarlem - there is an excellent bus service direct from the airport.
Another nice place to visit is Leiden which is on the main train line to Den Haag. A typical Dutch town with canals and windmills, plus lots of interesting-looking restaurants dotted around the town square.
Or, if you want to venture a bit further, there is Utrecht. If you are feeling energetic I recommend a climb to the top of the cathedral tower!