In 2005 I asked the same question. Lord Snooty, bless you, recommended sitges then.
I rode into Barcelona and asked 2 local coppers the way, my how they laughed, pretending to `mince` around.. strange thunk I.
Arriving in Sitges, tired and confused and discovering it was the Gay and Lesbian festival that week, I thought the ******* recommending this bloody place so I carried on and landed further south at Cunit. A lovely campsite next to the sea and have been there a couple of times since. (try it if you are in the area).
The year after I visited Sitges, I agree it is a lovely town but the ..er.. atmosphere and the ..er.. nightlife

put me off camping there (pun intended).
I was thinking this year of camping closer to Barcelona as Im picking the missus up at the airport then riding on.
Looks like Cunit again unless youve other suggestions.
By the way the campsite at Sitges was packed, not much room between tents.
Cheers
Hodge