Finally found a picture (by ejbaurdo) of our first Outer Hebrides beach:
This is on the Island of Barra; we sailed in, several years ago, on the ferry from Oban. Dumped off our stuff at a B&B in Castlebay, and went for a wander up the western road out of the town. Half an hour later, we find the beach pictured above.
We've been back several times since. There's an astonishingly ugly hotel at one end of the beach (how it got planning permission is beyond me) which has a quirky, but very good, bar restaurant downstairs with great views over the beach.