Any suggestions for registrars of domains that aren't .com/.co.uk/.net/etc.? I notice that a couple of those mentioned (Namecheap.com, Name.com and Gandi.net)

Any suggestions for registrars of domains that aren't .com/.co.uk/.net/etc.? I notice that a couple of those mentioned (Namecheap.com, Name.com and Gandi.net) offer this service, but is there a specialist registrar anywhere, or are these good enough? (I'm looking to register a number of .nl domains and have no idea where to look in terms of quality registrars.)