What does Jesus mean regarding "Raca," and "you fool?" - is he contrasting them? Matthew 5:22, KJV says


  But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment: and whosoever shall say to his brother, Raca, shall be in danger of the council: but whosoever shall say, Thou fool, shall be in danger of hell fire.


The final two clauses are separated by ": but" which indicates that they are in contrast with each other. Hell seems worse than "the council" - does this mean that saying "you fool" is worse than calling someone a forbidden term of contempt ("Raca?")
I looked at other translations than the KJV, and I found where the clauses are separated by "and" instead of "but." This indicates that Jesus is somewhat repeating himself for emphasis, and perhaps even saying that they are nearly as bad as each other.

The NIV says:


  But I tell you that anyone who is angry with a brother or sister will be subject to judgment. Again, anyone who says to a brother or sister, ‘Raca,’ is answerable to the court. And anyone who says, ‘You fool!’ will be in danger of the fire of hell.


Young's Literal Translation says:


  but I -- I say to you, that every one who is angry at his brother without cause, shall be in danger of the judgment, and whoever may say to his brother, Empty fellow! shall be in danger of the sanhedrim, and whoever may say, Rebel! shall be in danger of the gehenna of the fire.


In conclusion, Jesus is saying being angry at people without good reason, calling people forbidden epithets, and simply saying "you fool" are all things that should not be done.