I'm studying for the TEAS over the break. I started out just using McGraw Hill's 5 TEAS Practice Tests book, but I realized that some concepts I just didn't understand. Then I bought ATI's study guide and have been using it for the past couple of days. It is great! It actually explains every concept (e.g. a theme is..., the parts of speech are...) and includes many examples. It only has two practice tests, so I'm still glad that I bought the McGraw Hill book. I'm using the McGraw Hill tests as practice after I read each section. Once I review everything I'll have three practice tests left, two from the ATI and one from the McGraw Hill.
At first I didn't want to spend so much on study guides, but Amazon will buy back the ATI manual for almost 30 bucks I think, so in the end it won't be too much. Besides, the nursing school I'm applying to will only take your first score.