There are lots of books that can function as powerful resources for magicians, from my own, wide-ranging Modern Magick or The Complete Magicians' Tables to books going into depth on more specific topics such as Geomancy in Theory & Practice, Hands-On Chaos Magic, or Magickal Self Defense. In my experience, however, many magicians today don't start research into magickal practices by going into their book collections; some, quite frankly, don't have many books at all. Instead they depend upon that ubiquitous internet repository of information, Wikipedia.
I love Wikipedia. I think it's a great tool. But as I have repeatedly pointed out, Wikipedia is a great place to start research but