Glastonbury
Any of the New Forest sites really. If you have kids - go to Hollands Wood - there is a massive meadow at the front to play games, and you can walk to Brockenhurst - and there is a fish and chip shop and chinese there if you don't fancy cooking. Take your bikes.
I shall be camping at the Big Chill festival in August and it will be terrific.
Going to Vendee for the first time this summer so hope it proves as good as being said!
Cheers - I am going to go in a two weeks time, just need to get a new tent first!