Black Sheep by Georgette Heyer (I've read a lot of Heyer's books, but I think this one is my favorite so far because of all of the witty dialogue. It would make a great romantic comedy!)
A Skeleton in God's Closet by Paul Maier (What if someone discovered the skeleton of Jesus?)
The Eyre Affair by Jasper Fforde (Thursday Next books as movies? That would be amazing!!)
The Night Circus by Erin Morgenstern (This would make such a good movie!)
Shadow and Bone by Leigh Bardugo (These should be the next big YA movie blockbusters, right? First Hunger Games, then Divergent - now the Grisha!)
The Menagerie by Tui Sutherland & Kari Sutherland (Surely CGI effects can handle griffins. Kids would love this movie - and so would I.)
Hood by Stephen Lawhead (The King Raven series is essentially a plausible version of Robin Hood, set in Wales. Who doesn't like movies about Robin Hood?)
Garden Spells by Sarah Addison Allen (I love the genre of magical realism, and I think it could translate to a movie really well.)