Some of the most enlightening reading I have borrowed or bought have been books by Bishop Kallistos Ware, namely The Orthodox Church, The Orthodox Way and The inner Kingdom.
My favourite writer on Orthodoxy is Heiromonk Seraphim Rose. he wrote a lot about dealing with Orthodoxy and Secular society (which is something I have struggled to balance in the past) My favourite of his books is
Orthodoxy and the Religion of the Future.
Of all I would say my favourite actual book is "Youth of the Apocalypse and the last true rebellion" which looks at youth culture and Orthodoxy. it mainly looks at how people live, the effects and how Orthodoxy helps. It is very blunt on the subject too, which makes it even better.
Apart from that i just tend to pick up random books on the lives of the saints from online bookstores (They are usually about $1 on American sites) which lead me to read about other saints mentioned in the book, a bit like a treasure hunt.
"The true Christian is a warrior making his way through the regiments of the invisible enemy to his heavenly homeland." - St Herman of Alaska.