Michael Horton is a very good Reforned (Calvinist) theologian, I have read his other books on covenant theology and Christless Christianity (an attack on therapeutic deism which neglects the Glory of God) which I found very useful in my spiritual journey.
John Piper is a Baptist pastor who is also a Calvinist, he is a very passionate preacher who has developed the concept of "Hedonistic Christianity" which basically means it is easier to reject sin if we take delight from following God's commandments instead of falling for the false promises of sin.
I am sure many of you are already familiar with Cardinal Sarah and Scott Hahn - if you are not, then I highly highly recommend you check them out as soon as possible!! Wonderful authors.
I have been waiting for ages to be able to afford the book by Ralph Martin. It analyses the spiritual life using the writings of some of the most influential spiritual writers of the Church who are also Doctors of the Church : St Augustine, St Bernard, St Catherine of Siena, St Teresa of Avila, St John of the Cross, St Frances de Sales and St Therese of Lisieux.
What a wonderful compendium of spiritual writing!! The book is divided into the traditional 3 paths of the spiritual life - purgative, illuminative, unitive/transforming union.
Time to get into some deep spiritual reading.
I buy all my books through bookdepository.com they have most books in stock, are cheap and have free delivery. I live in Australia so the free delivery makes this a much cheaper option for me than Amazon. Plus the books only take 2-3 business days to be dispatched and then 5-8 business days to arrive.