A few posts back I described an alleged contract with the devil in a 17th trial which resulted in a burning at the stake. Nowadays we're much more casual about the matter. One of the more well-known "Spiritual Satanists," Venus Satanas, describes the ins and outs of infernal pact-making in an essay on her website, and in the video below.
A Spiritual (or Theistic) Satanist is one who believes in the reality of Satan (though they tend to believe the poor fellow has been maligned by more traditionally-minded religious folks). This is in sharp contrast to members of the Church of Satan, who are atheists and believe in Old Scratch as a symbol of radical freedom and funny costumes and freaky sex and whatnot.