Jim,
On the French side and towards the north eastern end, Saint Étienne-de-Baïgorry, has a great Municipal site, very clean, very cheap and very close to the shops etc that you require.
Downside is that although the roads into the mountains are great, there are fewer trails (as mentioned above).
On the Spanish side (just. It's near the top of the mountains), in the small town of Sant Pau de Segúries is a camp site. It's a very short walk into the centre of the town/village. The site has excellent facilities with a bar and restaurant.
Only thing I'd say here is that its proximity to Barcelona and altitude mean that it's a weekend escape for Catalans in the heat of the summer. Many have semi-permanent touring caravan plots to which they flock on Friday's. Like most Spaniards, they are not known for being quiet and retiring when they're having fun.
I can supply the GPS data if required.
Edit: I should point out that I haven't been to the Spanish one since early 2005 and the French one since June 2006, so they may have changed a bit.