Almost any book you want to buy has multiple online Christian book reviews. Here are my list of the top places on the internet to find them. Each site looks at books from a Christian perspective and offers helpful reviews.
This resource is dedicated to helping Christians find and read the best books available. So many books are being published today that it is difficult to find which ones you can trust – and which ones are a waste of time. I refer to the Discerning Reader often. The Discerning Reader is owned by Tim Challies but features book reviews from many different people for each title. This second opinion angle makes it my favorite.
Find review not only the best Christian books, they also give helpful reviews on most of the best sellers. Many of these reviews are published in Christianity Today magazine.
The Theology Website
The resource offers many book review on academic and pastoral targeted books. They review less books than the above links, but sometimes get to books that no one else reviews.
This site offers less opinion and more statement of the books content and thesis. This may be helpful if you want a more objective review.