There are lists abounding for summer reading. Of course, reading preferences are entirely personal but here is a short list of some of my own favorites.
The Woman in White by Wilkie Collins - Old and classic. If you haven't read it yet, read it now. I highly recommend it. Although it was written mid- 19th century it reads easy and current. A real page-turner.
Passion by Jude Morgan - I had this on my shelf for eight!!! years before pulling it down. And then I found I couldn't put it down. Extremely well-written, I frequently found myself marking passages to return to and reflect on the ideas.
The William Monk series by Anne Perry - starting with The Face of the Stranger - I have read the entire series (detective, set in Victorian London) and loved each book. William Monk is a wonderful character - although not entirely likeable.
Anything (and I mean it) written by Georgette Heyer. My aunt - a woman of intellect and class - introduced me to the novels of Georgette Heyer when I was in my late teens. I have read, reread, and re-reread every book that I could get my hands on; I find them easily as enjoyable when familiar. Witty and sharp, full of fun and a great turn of phrase, these books are what I turn to when I want (or need) to escape from the cares of life or simply to let go and relax. They are laugh-out-loud enjoyable. Perhaps not high-brow but in no way trash.
The Private World of Georgette Heyer by Jane Aiken Hodge (biography) - read this first if you haven't read any of the novels. You will appreciate Heyer more for it. It is an easy biography - but maybe that's because I am such a huge Heyer fan.
That's just a corner of what I like but it's a good summer list.