My favourite is the C.C. site at Doldowlod, just outside of Newbridge on Wye .dave.
There is a lovely walk from the site along the River Wye, also it has a childrens play area. No shower block though but it does have electrics.
Its not far from the market town of Rhayader and the scenic Elan Valley and its dams(about 4 dams in total).
You could drive along whats known as the mountain road from Rhayader to Devils Bridge and have a ride on the Vale of Rheidol narrow guage railway to Aberystwyth, it takes 1 hour each way and from memory the price isn't too bad.
You may spot the Red Kites to, at Gigrin Farm, just outside Rhayader they have a feeding station where you can go and view them.
The site isn't that far from me so we tend to go there if we only have 3 days.