Last 15 minutes of boil: Crystallized ginger (homemade is much better)--approximately 4 oz for a 10 gallon batch.
In Secondary: I tried Grains of Paradise, Malabar Peppercorns, juniper berries, and peels of Lemon, Lime, and Grapefruit.
Good, but "muddled" result, IMO. I much preferred the yeast derived phenols and esters along with the subtle ginger flavor and aroma; so did nearly everyone else.