I really enjoyed this article by Lydia Sharp today. Her idea is that the first major goal of a main character must be somehow to preserve his/her concept of identity. I'm not sure I entirely agree with this, since my main characters don't necessarily do that - however, the concept of identity and its relation to a main character's story goals is really important. She also emphasizes that there should be a critical fit between the character's identity and the nature of the plot - they should be in the most extreme opposition possible.
Anyway, take a look, and you might get some good ideas.