First of all, not every good and worthwhile book was written by a Catholic. Classics, first-hand historical accounts and Greek Myths are examples of stories that can be good, are often part of a solid Catholic curriculum and will not necessarily be written by Catholic authors. Furthermore, there are many times when we don't know whether or not an author is Catholic - we have to judge by the book itself. This is especially true in the homeschooling arena where the Protestants have a lot of experience.
Textbooks are generally the most difficult type of book to judge.
It is generally agreed among Catholics that, whenever possible, it is best to use Catholic textbooks for the education of your children. There are two schools of thought with regards to where to turn when no Catholic texts are available. We also won't find it as objectionable to support their organizations financially. On the other hand, some would argue that secular texts are a better choice because it's much easier to point out the errors, whereas errors in Protestant texts are much more subtle and likely to be overlooked. I believe that both sides have important and valid points.