What are the big rivalries? I'm guessing that proximity to one another is the major reason for these rivalries as with most around the globe.
AFCA has a nice post on rivalries near the end of the "Eredivisie Club Info" thread. It's sticky'd near the top.
This are the main rivalries in Dutch professional football (if it's a 2nd division team I've put (2) behind the name): Ajax-Feyenoord (not really close, but they are the traditional top 2) Ajax-Utrecht and Ajax-AZ (however it's more a one way "hate" from AZ and Utrecht versus Ajax than the other way around) Vitesse-NEC Groningen-Zwolle Groningen-Twente NAC-Willem II Roda JC-Fortuna Sittard(2) Roda JC-MVV(2) Zwolle-Go Ahead Eagles(2) Telstar(2)-Haarlem(2) Excelsior(2)-Sparta(2) (both from Rotterdam, but they both don't have a real rivalry with Feyenoord) Den Bosch(2)-TOP Oss(2)
Ajax and Volendam are on friendly terms mostly. Volendam's promotion last year was greeted with a big smile in A'dam. Great away match.
My sense is that Volendam is one of those "small" clubs that Ajax fans admire (and are maybe just a bit jealous of, now that Ajax is a public company and plays in the Arena). Without a doubt, this is not a rivalry, as Feyenoord and FC Utrecht are rivals. Here's an excerpt from a match report on the tribute game played in January 2002: "The bond between the two clubs has always been strong, but will now be even stronger after this warm and respectful evening." http://www.ajax-usa.com/matches/01-02/0112.html
Hmmm... Groningen seems to dislike Heerenveen a lot, they have a big deal about being "the pride of the north". Or at least the Groningen supporters do, since the Heerenveen supporters are too "decent" or just too apathetic to do something back. Heerenveen is being praised by the media and their fans as the nations' "second favourite team", because their supporters are very polite and they're based in a small village, a village inhabited with less people than there are seats in their modern stadium, they have a trainer that has been with the club since the founding of the club and that kind of "cute" stuff. However, a lot of supporter groups from other teams are getting sick by all of this. They do not only take Heerenveen not serious anymore, they also do actions to piss of the Heerenveen supporters to see if they can notice any sign of life there. Some time ago, the Feyenoord players showed their back to the Heerenveen players and supporters when Heerenveen played the Frisian anthem, while the Feyenoord supporters whistled an made noise. There were even teams who wanted to play the Dutch anthem for them if Heerenveen insisted on playing the Frisian anthem, but it was regarded that that was too childish. Anyway, it's not a real rivalry, but a lot of (hardcore) supporters in Holland feel contempt towards Heerenveen.
Re: What about PSV? Read this wonderful post from AFCA https://www.bigsoccer.com/forum/showthread.php?s=&threadid=53365&perpage=15&pagenumber=1