Christian Book Distributors has been a place I have bought books ever since I was in grad school. It is without a doubt one of the best places to purchase Christian books. I just purchased a commentary (Ben Witherington III Socio-Rhetorical Commentary) and they had to option to pay with PayPal. I chose that option and went through the process only to get a message that this purchase was outside their (PayPal's) values.
No problem, I paid with a credit card, but thought it was worth mentioning this issue here.
Btw, I can highly recommend Witherington's work, this will be the third of this series I have purchased.