Idon't have time for a large post (even though St. Augustine is most deserving of one), but I want to at least point you in the direction of some resources that you can use to learn more about Augustine on his feast day.
The Catholic Defense Directory has an entire entry devoted to St. Augustine, with links to articles that approach him from almost every angle. The Directory is currently being imported into a new format, so it's a little ugly right now -- but the links are still there, and I think they are very informative and helpful.
Also see my two blog posts on Augustine: "Did Augustine Invent Original Sin?" and "Reclaiming Augustine".
St. Augustine, Doctor of Grace .... ora pro nobis!