Cumin seed, commonly used in Mexican cooking (comino) as well as a common ingredient in Indian and Malaysian cooking. Overused cumin becomes very overpowering.
Cumin is used in many, if not most chili recipes. For best results, toast whole cumin seed in a hot, dry skillet just until it becomes aromatic. Remove, let it cook, then grind it in a electric spice grinder or in a mortar and pestle.