Here are books I’ve found helpful. The list is not yet exhaustive; I will add to it as I dig through my library.
Writing the Breakout Novel by Donald Maass
A New York agent and successful author gives his ideas on what makes an author “break out” or go to the next level in his or her work.
Writing the Breakout Novel Workbook by Donald Maass
The workbook. If you can only get one of the set, get this! It addresses plot layers, subplots, how to get at motivations, etc. I use this workbook constantly.
Having sold 35+ successful novels in 5 genres since 2000 (an estimated million words a year — whew!), Lynn Viehl is an expert in how to make more efficient use of your writing time. To her you listen, padawan.
A workbook all about plotting!
The two-part book for the online writing class I’m taking (which you can take for free by joining Forward Motion, but I bought the books also because I want them for reference). These cover outlining, plotting, worldbuilding, writing tips, editing, submission, etc. Definitely worth the money.