The Law Of God was one of the last books I read before getting baptized in the Church. It served as a catechism that taught me both the broad outline of the faith along with curious little details such as how to use a censer in the home or what days prostrations can't be done in church. It was writt
Indication of the Way into the Kingdom of Heaven by St. Innocent of Alaska
God's Revelation to the Human Heart by Fr Seraphim Rose is a good book for catechumens. It was derived from a lecture that he gave to spiritual seekers of all kinds, so he touches upon some of the problems with the modern spiritual mindset and also puts forth the Orthodox mindset as a counter to this. His discussion on the Western desire for a big experience in our spirituality is very important, he speaks about how easy it is to fall into deception when you are looking for something special to happen. It's a great book for those who are looking for a brief look into the Orthodox mindset.
Nihilism and the soul after death by fr Rose are fantastic. Moreover on living sinply by st John Chrysostom. I liked C.S Lewis' screwtape letters too to get a perspective from the demon side. Lastly you can check out fr Spyridon Bailey's books all accessible via amazon.