Maybe one of the islands?

Ameland or Schiermonnigoog will be the least crowded of the Dutch Wadden islands, but Vlieland will also be lovely then, and is easier to get to by ferry.

Even Texel won't be really packed. Terschelling is also really lovely but parts could be full of teenagers, though it is easy to avoid them normally.

Zeeland beaches can get crowded if the weather is hot since they are handy for Rotterdammers. Likewise the beaches around Hoek van Holland, Scheveningen, Zandvoort and IJmuiden.

Otherwise try the Noord Holland beaches - up by Egmond or Castricum.

Zeeland will be crowded that time of year, especially with Germans. If the weather is nice, chances are most Dutch beaches are packed to the point where the country would tip over to one side if it weren't connected to the rest of Europe .

I disagree with herismij2 here, the islands can actually be packed with noisy sailors (or sailer-wannebee's) partying away until deep in the night if the weather is nice. You can reach the other side of the harbors by jumping decks from boat to boat. We've had a couple of nice days around Pentecost this year - the yacht harbor was full and over 100 ships had to dock in the worker's harbor.

Your best chance is going a bit south from Den Helder. Callandsoog, Petten, Egmond. Don't go further south if you're looking for quiet beaches.

Thanks so much to you both.

My initial research says the islands won't be packed during my chosen dates -- lots of places to stay in every price range.

A further south may work better for my itinerary, so I will check that, too.

The island's hotels won't be booked because sailors tend to sleep on their own boats

What I meant to say is: hotel occupancy is not a good indicator of how busy it will be at the island. Many will sleep on their boats, in tents on one of the camping sites, in holiday-homes and chalets on one of the large bungalow parks.

For example: Texel counts just under 14,000 souls but hosts 55,000 to 60,000 tourists at a time during high-season (922,000 paying guests per year). The island provides 47,000 registered hotel-beds from which by law a max of 45,000 may be booked at the same time (authorities say this never happened yet though). The other tourists sleep on board of their own vessels or stay elsewhere.

The (inhabited) islands:
Texel: 922,000 visitors per year, beach 28 km
Vlieland: 140,000 visitors per year, beach 12 km
Terschelling: 500,000 visitors per year, beach 20 km
Ameland: 554,000 visitors per year, beach 27 km
Schiermonnikoog: 300,000 visitors per year, beach 18 km

Source: http://bit.ly/L3JdUs (ecomare.nl)

Believe me, the islands are busy beehives during the summer. School holidays start June 30 (south of the country) and lasts until September 2 (north). Your planned stay will fall in the most hectic timeframe of the year there.

Off the beaten path: try wijk aan zee.

It's got quirky surfer culture, one particular hotel that matches that (Sonnevanck), It's relatively close to Amsterdam and Haarlem if you need access to the big city, and the Kennemerduinen, a beautiful coastal nature reserve is on the doorstep. Looking to the north you'll see the beautiful coastline, looking south you'll see a gigantic steel works, that is right next to the village.

http://www.hotel-sonnevanck.nl/

http://www.timboektoe.org/

perfect for a different beach long weekend imo.

Hotel prices will rise as the temperature rises! Many people wait until the last minute to book a room, just because our weather is so unpredictable!
Have you thought about Cadzand? Pretty quiet year round. Lovely, lovely beach. Or a bit further up north near Breskens, the beach at Groede. A hidden gem! Nothing else to see there but a lovely wide soft sandy beach. Don't tell anyone, 'cause this is our secret place.