According to
this thread by Photon,
this post by Flylock Shox was the 1,000,000th post.
For anyone wondering why the URL post count doesn't add up to the main page statistics post count there isn't really a proper explanation (that I could find) although BlackArcher101 explains it a bit on the last post of page 1 (post 20 for you 60 post per page people) of the thread I linked above.