Im going to Sonar (I go every year - my favourite), Summercase, Benicassim, also maybe Exit and Bestival and a few smaller ones inbetween.
Havent been to Glasto since 2003 after about 5 consecutive festivals there, really fancy it this year for some reason, but then its a bit much to fly back from Spain for it, not bothered for any other "big" Uk festivals, I tend to find they have lost all charm, the weather is crap, and the people/vibe are/is dull.