As an English teacher, the first place I normally look for IELTS material is in traditional text books. However, there is a wealth of information on blogs about the IELTS 2015 exam and I would say a few of the blogs are much better than most text books.
Students are also starting to shun traditional books in favor of online resources. All of the sites on this list have been recommended by students and it holds true that students who put in the extra work at home seem to do better than those that rely solely on lessons