Have you ever considered using Cliff Notes when assigning literature to your high school children? For real! The notes are great in helping you, the parent (not the student!), come up with topics for literary analysis. You could also use them to design tests on assigned books.
Most recently, Cliff Notes came in handy when my two oldest were reading The Tempest. Shakespeare practically assumes that you already know the characters in his play and it was a tad confusing for my kids. The Cliff Notes had a list of characters, describing their part in the plot. It proved to be quite helpful. I borrow the Cliff Notes from the library and have never purchased them myself.
If you want to save a trip to the library the check out these websites:
Penguin Group: Teachers' Guides
Thanks to Carol Maxwell who wrote much more extensively, and eloquently, on this topic in The Catholic Homeschool Companion.