Schevenining is the beach closest to Den Hague, and is a pretty popular spot, including the 'Jump Club' down the south end of the beach where kiters hang out. The other place I have been is also pretty popular - Oostvoorne, which is a flatwater inland lagoon sort of thing - the Dutch do a good line in these. You have to be a bit careful at Scheveningen - the usual: busy beach with lots of punters, (it is a wide beach though) and Oostvoorne is a big of a bugger to get out at now because they have shut the main carpark, so its a bit of a walk - but not far.
This is a link to the webcam on the beach:
http://www.hollandbeach.nl/scheveningenbeach/webcams.aspalthough it looks pretty uninspiring in the middle of winter.
You can have a look at this fishing page for some idea of what oostvarne looks like. It's near Hoek van Holland (which is where the ferry to England comes in)
www.fff-europe.org/meeting2005/meeting05_public_englisch.htmThere are other places to go - plenty of them..there's lots of flat water in holland, but I stuck to these two just cos I always went with other people. People also go to Texel which is a big sand island off the (north holland) frisian coast and the ijselmeer but I think this is more for offshore winds. Not sure.
It will be cold, but the important thing is to eat lots of rookwurst. The best thing is that Holland is that it small and so it doesn't take long to get anywhere, but remember, it's full of natives fired up on coffee you can stand a spoon up in and screaming about in small european cars, so if you are biking - take care.