Habanero chili
A small, lantern-shaped chili, usually orange, with very strong heat and a fruity, almost tropical aroma.
Fresh habaneros turn up in larger supermarkets, at farmers' markets, and in Asian, African and Caribbean grocers; dried, flaked or powdered, they are also sold by mail order. They are far hotter than ordinary chilies, so start with a small amount.
Substitute:
Scotch bonnet comes closest in heat and fruity aroma and is a near one-to-one swap. Thai or other hot chilies supply the heat but not the fruitiness.