Ok, seriously, how did I not know about this? There's a movie coming out in 2010 called Ramona and Beezus based on Beverly Cleary's Ramona books! The cast I'm unsure about-Selena Gomez as Beezus?-but I think I'm just biased because I remember the Ramona series from way back when with Sara Polley. I checked those videos out from the library all the time-as well as the Ramona books. So even with the strange casting choices, I'll still go see the movie!
Melissa De la Cruz's Au Pairs series had the move rights sold back in 2006, but a writer for the film has recently been hired, so a movie might not be far off! A movie version of Zoey Dean's A-List is also in development with Alloy as well.
Finally check out this trailer for I Love You Beth Cooper, based on the novel by Larry Doyle. I still can't believe my mom read this book-and liked it!