I have found that New Interchange hits on almost all of the types of content that IELTS does such as the environment, education, work, news, movies, food, people, etc. In addition, it is teaching skills for reading, writing, listening, speaking.
Of course, as I have said, New Interchange is all that I have been able to find that fits the the need of teaching skills and content so well for IELTS. But I really would like to hear the titles of other books that are also good in a general way or covers some specifics. I heard Headway is similar to New Interchange although perhaps it is not as comprehensive with so much supplimental material.
At this point I would also like to clarify my strategy for teaching IELTS.
1. ENGLISH SKILLS: If there's enough time, work to improve the student's English level through English training such as we have been discussing.
2. TEST PREP: Help the student gain an understanding of how the IELTS test functions. There are various books that deal specifically with the IELTS, how the speaking part works, the two tasks of the writing part, etc. (I always teach my students how to do a 5-paragraph essay for the 250-word Task 2.)
I think of it as two courses and think it's best taught as two courses. The first one is actually teaching English and the second one is teaching how the functions of the IELTS test works. The second one can be a short course and it's rather easy for the students to get the point of how different parts of the test work. Once they have this test-prep course they should understand it.
I believe this one bit of training can help a candidate improve their score by one band level. I suppose some people would question that assertion so let's look at it another way. This training can help a candidate avoid making mistakes that could cost him one band level.
Now if they should fail to get the score they want in IELTS they do not have to take this second course, the test-prep course, again. Not scoring high enough, means that their English level is not high enough and they need to work on their English skills which is a much bigger job.
For this effort I have used various test-prep books for IELTS. All of the ones I have tried have been useful but I guess I wasn't relying on them so completely, using them more as a framework to work from, as I have a lot of things about the test that I have learned and use that as a resource when teaching IELTS. So I have no strong recommendations to make on IELTS test-prep books but am interested to hear other's recommendations on those as well.