Which coast are you looking at? In the South close to the Spanish border I like Colliore for the scenery, but the beach itself is small. The pays basque is nice for big beaches and big waves, but of course the water on that side is colder.
The beach in Sete is not bad if you're looking for sand. Colliore is on the med side, btw - I wasn't that clear. There's a wider beach nearby called Argelès. I've heard Saint Cyprien is nice but never been there. I don't know any sandy beaches in the Cote d'Azur but I hope someone else does!
if you want wild beaches or family and with amenities like showers. It also depends on your budget.
Cote d'azur will be more pricey, Languedoc roussillon more reasonable. Collioure and Argeles, I don't know but they are supposed to be really windy beaches great for windsurfing or kite surfing. Between Sete and Montpellier you've got a cboice of wild or not neaches. Around marseille, like cassis it's more for the scenary as is by toulon, hyeres or frejus.
Ah yes, Cassis is nice! And Saint Cyr sur Mer in the Var....It's true that the beaches down the coast from Perpignan can be windy...depends on luck really. Have you thought about Spain? The beaches in L'Escala are great - Montgó is really big and sandy and protected from the wind because it's in a kind of cove.
My advice? Hop on a boat in Marseille, Toulon or Nice and head for Corsica! (Confession I am a bit biased)
Corsica has fabulous long white sandy beaches down the east coast, whilst the west coast has pretty beaches in coves interspersed with dramatic mountainous sheer drops & scary coast roads. The Cap has pretty fishing villages, Bonifacio has stunning white cliffs looking out over the nature reserve of the Iles Lavezi ..... and the weather's invariably nicer than on the mainland ......
.... and I happen to know where you can rent reasonably-priced self catering chalets