I am traveling to Spain in late May with my family. Our travels will take us from the San Sebastian area to Barcelona and then on to Madrid. As we are traveling by car train access is not critical. I am looking for recomendations for a nice beach resort within 4 hours of Barcelona to spend two restful days before we head on to Madrid and ultimatly depart for home. We have little need for nightlife beyond dining. I would prefer less crowded areas, but something to do aside from watching the surf. Thank you all in advance.

Sitges

I second it, SITGES.

It looks from previous posts like stiges is primarily a gay destination.I was thinking further afield.

There are plenty of beaches in the way to Madrid, by Valencia instead of by Zaragoza. The Valencia route is 40 km longer than the Zaragoza in 650 km so no big deal.
Sitges is fine for a beach day if you are in Barcelona but as said there are many other alternatives.
Just to name some:
Salou, 10 Kms south Tarragona, nice and big resort. close to Puerto Aventura.
Cambrils, some 10 km south of Salou, same beach but quieter place.
San Carlos de la Rapita, 100 Km south of Tarragona, This is a small fishing village, with old style vacation, little restaurant by the port quiet beach, relatively small hotels. Not very fancy but cute.
Benicassim and Oropesa in Castellon, nice big beaches.
In late May you should have no problem with hotel rooms and with some luck weather will be just fine, sea water might be a bit cold.