I'd agree with others that a bad selection will actively put kids off reading even more than they already are!
Having said that, if we are going to have some required reading I'd add in one from every genre, including non-fiction. My schooldays completely turned me off period dramas for the rest of my life, because every damn book we had to read seemed to be about wealthy socialites set in the 17th and 18th century, doing the most mundane and boring things I could ever imagine! How was I ever supposed to be interested in that kind of literature? Variety of any kind would have been a big plus.
Non-Fiction: A short history of Nearly Everything, Bill Bryson - I'd recommend that to everyone actually, not just kids. It should be required reading for anyone wanting any form of public office, considering how lacking in knowledge of reality most of those people seem to be!
Fantasy: LOTR, Tolkien (obviously!)
War/Military/History: Catch 22, Joseph Heller
Sci-fi: Neuromancer, William Gibson
Comedy: Pretty much any by Terry Pratchett. Night Watch would probably be my favorite, but not necessarily a good place to start?
Oh and a collection of short stories wouldn't be a bad one to force kids to read - even in the days where school was doing its best to put me off reading completely, I would happily read through a sci-fi anthology of short stories in a single night - it's also likely to be a lot easier to set homework around a complete short story rather than on a chapter of a novel that feels to most of the class like it's been going on forever without going anywhere!