To celebrate their 10.000th Facebook 'liker', NS currently has an offer which allows you to buy a day ticket + a free drink at a beach club in Zandvoort for €10 (instead of the regular €16).
With this ticket you do not actually need to go to Zandvoort, but you can travel anywhere in the Netherlands with NS trains (no regional carriers such as Veolia). Book through their webshop: http://www.spoordeelwinkel.nl/product/strand You can only book 1 ticket at a time and until 27th May only. The ticket itself is valid until 20th June! At the beginning of your booking they will state a price of €16, but after filling in your name etc you'll be able to enter the promotion code "FAN2012", which should lower the price to €10.
They claim the offer is only for the first 500 people who buy the ticket, but I have just bought one myself, so it's still possible.