Christian Liars

For many years I have wondered what sort of rationalization it takes for Christians to tell lies. Somehow lying isn't that much of a sin in Christianity. It's seen as somewhat of a Santa Claus thing, it's OK to do it as long as someone benefits from it. But why? Why isn't lying just as much a sin as any other sin? Why doesn't the truth matter for Christians?
If you approach a Christian with this thesis, she will deny it. She will look at you as though you've lost your mind. She doesn't lie. Bush doesn't lie. McCain doesn't lie. Palin isn't telling lies. But in even my own personal experience working for Christians and having Christians in my extended family, I know how easy it is for these Christians to repeat obvious lies. And the lies clearly benefit the liars.
I'm not talking about run-of-the-mill liberal Christians here either. I'm talking about Bible-thumping right-wing "fundamentalists" who point fingers when they see sinners. I'm talking about right-to-lifers and anti-gay activists, people who are delighted to commit themselves or their children to the mission field. I'm talking about solid "family values" Republicans. I'm talking about people who you would think would know that the Bible doesn't advocate lying. Or am I wrong about that? Does the Bible justify lying for Christians? If so, where? Give me book, chapter, and verse.
This weekend something relating to this occurred to me that I hadn't really paid much attention to before.
Years ago, fundamentalist preachers used to preach and write about how Christians need to separate themselves from the world. God's domain is heavenly. The world belongs to Satan. Christians need to separate themselves from Satan's realm, die to it spiritually, and be born again into God's heavenly realm, not through physical death but through the "born-again" experience of salvation and righteous church-based living and fellowship.
I don't attend church anymore, but in the trailing years of my church attendance there was some controversy over that concept of separation. It was argued that Christians couldn't effectively witness to the "unsaved" if they were separated from them and if they held themselves to somehow be living more righteously when in truth we all know we are sinners. Salvation-based righteousness seemed hypocritical to the unsaved even if not to the saved. Because of this controversy, the idea of Christian separation from the world slipped into the shadows. It became, for those who still believed it, something that was kept in the closet.
But the basic concept that there is God's heavenly realm and then there is the world has remained strong in right-wing Christianity. And it is clearly understood that when you pray or when you read your Bible or when you fellowship with your Christian brothers and sisters you don't lie. You are in the presence of God or the Holy Spirit when you do those things and lying in that presence would of course be a sin.
But outside of that realm, when you are in the world, dealing with worldly ideas and powers and problems, you aren't dealing with God. Satan rules the world. The Bible tells you so. So how can it be considered a sin to lie to Satan?
So I ask again. Give me book, chapter, and verse to justify telling lies to the world. Clearly you do it for your own personal gain. Explain why that is not tarnishing your soul when you do it, when you make that bargain with the Devil. We all stand at the crossroads every day, every moment of our lives. We all face the same temptation - join Satan in the bargain and gain personally in the world or stand with God and your commitment to truth and suffer the consequences. Where in the Bible are you told to strike that bargain with the Devil?