I do not teach junior high, but if I did, two books I would place high on my list would be: The Bronze Bow by Elizabeth George Speare and Twice Freed by Patricia St. John. Both are historical fictions and both also set the stage for discussions about real life issues. Three others (of different genres) that I would consider worthy of a story time list for junior high level are: Big Smoke Mountain by Lewis Miller, Watership Down by Richard Adams, and Trapped in the Old Cabin by Patricia Kershaw.
A number of years ago one teacher told me how he intentionally chose a wide variety of genres to read from — humorous, true stories, fantasy (such as The Narnia series), missionary stories, etc. I thought that was a good idea and have attempted to fashion my story time list with that in mind.
I sent an email to a couple teachers asking what they would recommend, so I might have more to add here in a few days.