Unfortunately I don't believe there are any sites with comprehensive SANFL stats - the stats on the official SANFL site only go back to 2003!
If you want ladders from each year, going back to 1907, this is available at
http://www.thepowerfromport.com/sanfl_ladder.php?season=2005
(change the season for different years), plus that site has detailed information on every player to ever play for Port. Note that you need to create an account at the site to view it though.
As Wedgie said, there is some North-related stats at
http://www.rocketrooster.com, and
http://u-dogs.net/ has the results of every Centrals game ever.
But that is about it as far as I know... Mark Beswick used to have a comprehensive stats site, but this hasn't been operational for a few years now.
A lot of statistical information will be included in Phil Herden's SANFL Media Guide, which will be out by the start of the season. I have been helping check the stats for this book - I'm currently going through checking all the head-to-head records for all teams against all opponents at all grounds.