Reading is a very subjective activity and what pleases one person, can put another person off completely. Personally I like biographies, autobiographies and crime novels. I like (auto) biographies for the insight they give into another person’s life and the stories told can be very inspiring. I like crime novels because, when they are well-written and well-researched, they give an idea of human motivations. Many modern crime writers also paint an excellent picture of the country and culture they are writing about.
For use with students, I like the series of readers edited by Philip Prowse. These are readers written with adult interests in mind whilst still using simplified language. They treat students who are learning as intelligent people with adult interests; the stories are not patronising.
I have also successfully used plays by Willy Russell (e.g. Educating Rita and Shirley Valentine). The language is contemporary and colloquial. Plays are useful because there is a lot of dialogue rather than description as is found in a novel. I don’t know if a simplified version exists of these plays. If you took the original version, I think it would be very challenging for an upper intermediate level.
I think it’s important to check what your students enjoy reading. Do a questionnaire or class census to find out which genres they prefer: maybe biographies, historical, crime, etc. If students have some say in the choice of story, they are more likely to be motivated to read.
Think about how people generally choose something to read. They are more likely to read something they have already heard about; this could be because the subject is topical or because the writer is known to them.
Also consider the level. In general terms, students can read at a higher level than the language they produce. When they are interested in the topic, they will make more of an effort to understand. A tip to help you choose the right level is to copy a paragraph from the story and to blank out, every sixth or seventh word. If students can still understand the paragraph, they’ll be able to cope with the book.
Whatever you choose to do, we would be very interested to hear about how it goes. You could post something in one of the Tefl.net forums.