One of the most helpful free audio resources in the last seven years has been Wayne Grudem’s lectures through his excellent Systematic Theology. He began this lecture series in 2005 at Scottsdale Bible Church and finished in 2009. The series was built around the reading of each chapter and Grudem’s lectures followed the readings. I recommend you purchase his Systematic Theology to coincide this lecture series. It is one of the most readable and accessible Systematics I’ve read. Grudem’s lectures are clear, insightful and he is very helpful in laying out all positions on certain difficult and controversial issues. They are all followed by a short Q&A session.