Many summer reading books, for higher-level secondary English classes, are not decided by the teacher, they're just accepted as being part of the curriculum nation-wide. I've never had summer reading assignments, but here are the pieces of literature I read the past year in my Engilsh classes:

The Scarlet Letter
Brave New World
Frankenstein
The Awakening
Hamlet
Oedipus the King
Much Ado About Nothing
A Midsummer Night's Dream
Othello
Dracula
Invisible Man

I think those are all of them. The only one I found particularly depressing was The Awakening, where (SPOILER)The "heroine" gets madly depressed about her life, has an affair, and eventually drowns herself.