Does believing in Jesus Christ save me, or do I have to do something more? James 2:17 says that faith is not enough. Does that apply to salvation? Is belief (or faith) in Jesus Christ enough to be saved, or is one expected to act on that faith? If works are required for salvation, what is the threshold of that action. Does this threshold vary by denomination?
This question cuts to the core of an apparent conflict between the teachings of James and Paul. Here's some of the relevant scripture:

James 2:17-18, 24 (NIV)


  17 In the same way, faith by itself, if it is not accompanied by
  action, is dead. 18 But someone will say, “You have faith; I have
  deeds.” Show me your faith without deeds, and I will show you my faith
  by my deeds. 24 You see that a person is considered righteous by what
  they do and not by faith alone.


Ephesians 2:8-9 (NIV)


  8 For it is by grace you have been saved, through faith—and this is
  not from yourselves, it is the gift of God— 9 not by works, so that no
  one can boast.


On the surface, it seems that James states that it is works, not faith that is the ultimate source of imparted righteousness. while Paul clearly states that works are useless and only through faith is righteousness and salvation attained.

The key is to put these writings in their proper context.

Paul in many of his writings is addressing Jewish Christians, those who came from a fairly orthodox religious background. Orthodox Judaism is highly legalistic and works-oriented, believing that salvation is achieved through strict adherence to the law. When Paul is talking about "works", he is referring to the legalistic code of Old Testament laws that continued to be a stumbling block to early Jewish Christians. And he is clear that adherence to the law is not a path to salvation. Only faith in Jesus Christ, who fulfilled the OT law with His death and resurrection, leads to salvation. Jesus' freed us from the bondage of sin as laid out in the law.

James on the other hand is addressing a different audience... he is addressing Christians who have faith in Christ and yet have taken their freedom from the law to the extreme. They are claiming that because of their faith in Jesus Christ, they have no need of any law and can behave any way they wish without fear for their salvation for their faith is sufficient.

Jesus clear on the matter of how we should live lives of faith:

John 15:5 (NIV)


  5 “I am the vine; you are the branches. If you remain in me and I in
  you, you will bear much fruit; apart from me you can do nothing.


Christ dwells in us through the Holy Spirit, and the "fruit" of the Spirit is "love, joy, peace, longsuffering, gentleness, goodness, faith, meekness, temperance" (Galatians 5:22-23). These fruits are "works", not works that garner righteousness or salvation, but works that grow properly out of a life strongly rooted in faith.

And so you see there is no conflict between Paul and James. Paul is teaching legalistic Christians that salvation is only achieved through faith, while James is teaching Christians who use their faith to justify living sinful lives.

The proper life of faith (living branches of Christ's vine) will naturally tend towards good works (bearing fruit) and that if you don't see these works, you have to question whether their faith is authentic.