What are some good books against sedevacantism?

My advice is to stay away from sedevacantism itself. If you are looking for books that argue against it, the best work by far has been done by John Salza and Robert Siscoe; their website is trueorfalsepope.com, and Salza is spelled S-a-l-z-a. They have done the most thorough work of any of my colleagues on the subject.