I have a funny relationship to summer. Sometimes I love it, sometimes I hate it, but no matter what the books I read during summer become indelibly associated with this season. The Count of Monte Cristo is definitely one such book. I read it years ago, in seventh or maybe eighth grade, and I still associate it with summer. It's a fabulous book. For being a solid 1200 pages (please don't read an abridged copy), it is enormously readable and easily followed, despite the multiple simultaneous pieces of plot. And it has just about everything in it, romance and mystery and everything else. My favourite part was always where Edmond Dantes is in prison with the fellow whose name I can't remember, digging their way out and also learning all sorts of interesting things. Actually, my only specific memory of the time I was reading this book is that it was kind of grey and rainy the day I checked it out of the library, but nevertheless I associate it with summer. It's also, by being so big but also so little work, great for long summer afternoons.
Havemercy is also one of my summer books, I think, though I only read it last summer so who knows whether it will remain so. It's a fantasy novel involving giant metal dragons that have personalities despite being machines, and four different main characters who in various ways are all, or will be all somehow related. In my head the fantasy world of this book is all enormous blue skies and sandstone buildings, though I think this is not actually its setting. I read this on my way to and from working at Seattle Children's Theatre last year, waiting for the bus on the edge of a park in the sun, and in the back of the bus on hot afternoons.
I'm not sure why summer is so much more particularly associated with certain books than other seasons. It may have to do with Seattle's weather, which is pretty uniformly sunny and hot in the summer (at least in one's memory, not so much in actuality), but is entirely variable the rest of the year. The association is definitely with the sun and the distinct blue of the sky, and not with any other quality of summer.
For a few years I hardly read during summer (I can't for the life of me figure out what I did instead), but the past couple I've read a lot more, and this summer I'm especially devouring the books. It's nice to have time to read.