Undoubtedly, some artists have a talent for making music for the summer. I was only ever a casual Zutons fan, but they are just made for soundtracking the sun and the picnics and the joy of summer days out. I also feel that about The Coral (don't tell me you haven't smiled from cheek to cheek listening to In The Morning on the radio), The Holloways and the fantastic Yeti. There are others, but those sound like pure summer to my ears.
This year, it appears Belle and Sebastian are going to take the credit for the sunshine. I am several years late (again), but if you haven't heard them, I'd really recommend giving them a listen, while the sky's still blue and evenings are still light. They're 'harmless', if you want to be condescending...but I don't. They're indie pop at its most charming, lively and summery.