There are lots of great sites in the lakes, depending on what facilities you want will generally give an indication of how busy they will be, especially during holiday season.
If you want a quiet, scenic but basic site try Hollows Farm at Grange, on the Keswick to Seathwaite road, you can usually get on there during busy times. The Castlerigg sites just outside Keswick are great too but more facilities, great views etc means they are generally busy so book in advance.
I live nearby so can generally take advantage of quiet times when lots of the crowds have gone home.