When we started researching biodiesel we covered a ton of various websites, blogs, and forums.  By far the most impressive has been the guys over at Utah BioDiesel Supply.  In particular their video tutorials are packed with scientific facts and calculations that prove to be a great base of knowledge for the 'Big Picture'.  We find ourselves visiting the site often to get quick reminders about titration measurements and final testing procedures.  They also have a wide variety of supplies for those things you can't find at Wal-Mart or Home Depot.