Cardamom. I acquired the habit from a ninety-something Yemeni gentleman who also hooked me on Yemeni Moka. If you haven't any cardamom already, note when shopping that the bright white pods have been bleached and bleaching can diminish quality. If you get to open a sample pod before buying, try to find seeds that are black and oily. I have had excellent luck with cardamom from India and Guatemala: far better than the bleached Spice Island or Schilling stuff and at an eighth to a tenth the price. Try Indian, Pakistani, and southeast Asian groceries.
To put into coffee, I also favor the cheaper Irish whiskeys, aged black rums (Old Monk 7 year old from India is a current favorite,) and brandies (Paul Masson VS is surprisingly drinkable for the price.) Higher grade liquors go into snifters on the side, of course.