Here we'll keep a list of resources specific to Bullet Journals. I'll update the main list with any recommendations posted in response to this thread. Later I'll try to break things down more like putting legends or Indexes in their own row as everyone has different preferences in that regard on how complicated or simple they prefer their journal to be.
Bullet Journal [site/blog ran by creator Ryder Carroll]
My Pinterest folder [saved things here from various index/legend types to layouts to free resources]
Legend Option [a tumblr user shares their legend]
Starting A Bullet Journal [a blogger named Sarah shares how she's been using hers to help people figure out their own]
How to Use a Bullet Journal for Better Mental Health [a really handy Buzzfeed article]
24 Tips to Make the Most Perfect Bullet Journal [found on Pinterest and seems popular]
3 Steps to Starting A Simple Bullet Journal [found on Pinterest and sharing as for some starting simple is better]
3 BuJo Spreads That Have Improved My Reading Life [handt piece on Book Riot, specifically to help people read more]