Phillip J. Long has recently had several relevant posts considering the question of the relationship between Acts 15 and Galatians. You can check them out on his Reading Acts blog.
In chronological order:
Issues at the Jerusalem Council: Circumcision – not surprisingly he concludes: “this survey indicates that the practice of circumcision was one of the most important issues to Jews of the first century.”
Acts 15: Who were the Judaizers? – he believes there were Jewish Christians, likely Pharisees.
Dating Galatians – Before or after Acts 15 – he believes that Galatians is prior to the conference.
Today saw him post on Galatians 5:17 and Legalism.