Do you mean sites that have barely any facilities?
We stayed at a great place down along the side of the Mawddach Estuary - on the way to Barmouth. Little place called Bont Ddu. The site is dead near the edge of the shore so you can hear the water come in and go out at night. There's sheep walking wild around the site too. And the farmer sells big bags of firewood and let's you make fires outside your tent. It was fairly cheap per night too. Map
Zoom out one level, its the little blue tent.
The farmers name was Bryn Lloyd but its probably his son running it now. I found the number: 01341 430644.