The most bitter list on the internet!
This page indexes the bitters recipes I have unearthed online, with tasting notes if I have tried the recipe personally.
Aromatic Bitters (must be 21 to enter site)
Blood Orange Bitters (I make this one regularly! The quality of the blood oranges greatly impacts the result of the finished product. I enjoy a few drops of these bitters in whiskey & club soda.)
Creole Coffee Bitters (must be 21 to enter site)