Good tips given here allready. When you go for the culture, a nice festival to visit is the "Zwarte Cross". It is the biggest Motor Cross festival in the world, but i think also one of the weirdest. Lots of stunts, beer and farmers. The music is very divers.
Little clip of the Zwarte Cross (Black Cross).
http://www.youtube.com/watch?v=IdTA0nKzX...re=related
It is a cheap festival, for 20 euros u have a ticket and fun for a whole day. (The day after not, i think xD)
Disadvantage: It is on the country side, not so easy to reach. (2 hours of driving)
http://maps.google.nl/maps?f=d&source=s_...410767&z=8
I think it is good to check on youtube what you think about it.
Obi posted som realy good tips, i think DefQon is the best to go to. Unfortunately never been there, but i always buy the aftermovie DVD`s and there are always people from all over the world. You will find the best Dj`s in the world there and what i`ve heard from people i know it is worth a visit.
When you come to Holland and stay there for a weak, you can visit more city`s then Amsterdam. I`m from the north off Holland and when i go to the city, i like to go to Den Haag, Rotterdam, Alkmaar, Deventer and Arnhem. It is very easy to go there with the train and it is not so expensive. On this site, you can plan your journey and see the prices.
http://ns.nl/cs/Satellite/travellers The (most) people in Holland, can speak English (for a bit), so you always find someone who can help you with some problems.
In the big city`s you can find internet café`s so when you`r on your vacation you always aks for visiting tips and shelters here i think.