I'm asking this since I've already found myself in two minds a couple times about how to refer to a book when answering a question.
I've seen many people link to Google Books previews, when available, to show specific passages of a text. I've also seen people link to Amazon. By the way, it looks like Amazon links get automatically reformatted by the SE software.
If the work is freely available online, like Hatcher's or Milne's books, then I would definitely link to the author's web page. Similarly for articles on ArXiv. But otherwise, how should I refer to a book or an article?