Amazon search (UK), will show you that there are over 1,000 TEFL books available to buy online. Of these 1,000, you can filter four stars and up to try and narrow down your search to the quality books.
Thanks to Amazon, I now have over 182 books to choose from which readers and reviewers think are pretty good, however, in reality, there are much fewer quality books in there as the title suggests.
The types of books available seem to vary. Instructional books generally come from TEFL institutions and course providers. The aim of these books is to break down common terminologies, teaching techniques and industry theory, into bite-sized information so you can pass a test or use them at short notice in class.
For English teaching, you can also find some more subject-focused books. These books focus on more in-depth ESL methodologies and practices. For example, teaching phonology, grammar and even language acquisition.
As well as instructional books for future teachers, you can also pick up some “true story” books, or “how to get rich books”. These seem to be more sensationalist stories about adventures abroad. There is no denying that there is a lot of fun to be had, but after reading the opening paragraphs, of a few of these publications, it seems like stories are exaggerated, or interesting pieces that you can find on a blog anyway.
To buy or not to buy is indeed the question. I believe the answer this question ultimately depends on you. I have bought ESL books in the three categories that I have mentioned, but I find longevity to be the ultimate decider.
Most of the books from TEFL schools and online platforms tend to be instructional. They have digestible content, and they really help with any test coming up. I have three of these books, and I mainly used them when I was going through my 120-hour TEFL course. Since then, I haven't picked them up. My feeling is, you don't need to buy one. The information you need is available for free online, you will have most of the information in the course, and the likelihood is that someone, whether a person or school, will give you one for free. These books do have their benefits, they are useful, but I think you'd be better spending your money somewhere else.
Academic books seem to be a different beast. These are the books that seem to be more rooted in science and theory and give way more detail on topics such as grammar, phonology, language acquisition and related subjects. In the long term, these are by far the most useful. You can really use these books to take your understanding of what you're are teaching to a much higher level, and you'll be better placed to answer the tough questions students ask. However, I think the timing is more important here. If you are just starting out in the ESL industry, buying a book that dives deep into a topic such as how to teach phonology, maybe a little overwhelming in the beginning. Especially when you are trying to master some of the basics, like classroom management or concept checking questions.
For these books, I'd say go for it but don't bite more than you can chew. Get the basics down, and then work your way up to the more complex stuff at a later date. Finance wise though, go for second hand. They will be much cheaper, and they'll do the job.
Since the advent of the E-book, there seems to be more and more of the “TEFL story” books. Most of them are the self-published exploits of someone who had “the experience of a lifetime” or someone who “made a fortune teaching English as a foreign language”. The stories themselves are pretty good, but I would only read one if it were free. There are tonnes of blogs on the internet with amazing stories, pictures and videos. They often share some great advice on everything related to teaching English as a foreign language. I personally like Don's ESL adventures, but there are many other cool blogs out there.
After reading this post, you should feel a little more informed on the types of TEFL books available, and whether you should buy them or not. I wholeheartedly believe that the final decision is yours, and depends on your circumstances. For me, they all have a value and purpose, but see what you can find online first, and even wait until you start teaching. You'll find many schools already have these books and they'll be more than happy for you to borrow them.