C. S. Lewis
I should have put an asterisk by the question about Lewis, in case anyone is not familiar with him. The link below tells of some of his doctrinal errors (thanks Toonces).
The Screwtape Letters serves the purpose of illustrating how subtly the enemy can fool us. Most Christians don't realize how thoroughly hated we are by the forces of evil, and how diligently they work toward our downfall. The Screwtape Letters does a good job of showing the lengths to which Satan will go to trip us up.
It's very difficult to find a prominent Christian leader these days who doesn't have a major blind spot in one area or another. I am amazed at how well they can know the scriptures in most areas yet fall to the ground in others. I can only hope and pray that by continually bouncing my ideas off others that any deficiencies will be exposed so I can deal with them.
Universalism is a huge problem here in the Zone. I have pretty much left the Religion forum to them so they can vent freely, but they know where to turn if they ever consider that they might be wrong. At least most of them don't pretend to be Christians.
www.trinityfoundation.org/reviews/journal.asp?ID=205a.html