Poll on New Physics/Math Book Topics

For readers who are interested in reading math/physics books, I am interested in what people are interested in as far as topics. Some things I am considering are:

• Partial Differential Equations
• Ordinary Differential Equations
• Math Methods for Physics
  

Also I am thinking of bypassing the traditional publishing model, and selling the books as ebooks available directly from this site. Let me know what you think about that.