I'll post on a spirit that seems, at least to me, to be a natural progression in spirits taste from bourbon, and that is aged rum.
One of my favorites has been Angostura 12-year (Trinidad), but I recently purchased a bottle of Mount Gay Extra Old (Barbados)-- a collection of batches aged up to 17 years. I got it at the State Store for $45/btl.
IMHO, this is one of the better aged rums. While it does still have a gentle burn to it (which most bourbon drinkers should be accustomed to), it is quite refined, with ample notes of vanilla, caramel, nutmeg, and allspice. There is also definitely a hint of butter toffee in the nose-- in fact, the nose of this rum has a unique "buttery" quality that I haven't experienced in any other rum as of yet.