I have many that have never even been optioned. For a bonus, at the end of the article there's a list of the five best and five worst screen adaptations. Thanks to Gerard Saylor for the link.
Why so many novels never make it to the big screen - Independent Online Edition > Features: "The cinemas are full of turkeys yet that brilliant novel you read three years ago has never been made into a film. Danuta Kean descends into development hell and finds out why so many authors get trapped there."