2 Cor. 11:14 (ESV)
…  for even Satan disguises himself as an angel of light.

1 Peter 5:8 (ESV)
Be sober-minded; be watchful. Your adversary the devil prowls around like a roaring lion, seeking someone to devour.

Ephes. 6:11 (ESV)
Put on the whole armor of God, that you may be able to stand against the schemes of the devil.

A promo video from Focus on the Family regarding their audio series of C.S. Lewis’ “Screwtape Letters”.

[youtube=http://www.youtube.com/watch?v=FLfYd2nd5NI&feature=player_embedded#!]

You can order it here