At the moment I'm working on a new book, a YA contemporary with just a hint of something out of the ordinary. It's a standalone title and unrelated to my other books. I'm also cooking up something a bit different, but I'll see how it comes along before I say too much about it here.
I'm always swamped with plans and plots and notes covering both completely new ideas and the awesome collision of old ideas that on their own don't make a story, with some new notion that combines to make something exciting. I'm nearly always working on multiple projects, but I usually concentrate on putting down the words on just one at a time. Although, I'm considering experimenting with running two books in tandem, so we'll see how that goes!