What blessing is said for a scent not from a tree or herb, e.g. perfume?

For pleasant scents that come from non-plant sources, such as perfume, synthetic fragrances, or scented oils not directly from a plant, the blessing is 'Borei minei besamim' ('Creator of various spices/fragrances'). This is the most general fragrance blessing and also serves as a 'catch-all' when you're unsure of the scent's origin. It is also the blessing used during Havdalah when smelling the besamim (spices).