See Jonathan Klawans article entitled "Was Jesus' Last Supper a Seder?" hosted at the Biblical Archaeology Review website here. Although I disagree with Klawans' conclusion that the Lord's Supper was not a Passover Seder, the article provides a decent overview of the issue. I would also suggest that readers take a look at Harold Hoehner's Chronological Aspects of the Life of Christ, pp. 76-90.