I found this excellent website featuring a few specialty incense formulas for African derived magical practices. The same website has some other recipes for oils and powders and things.
While the word "spell" theoretically suggests a written charm to produce magical results, anyone who knows about modern practice is aware that the term spell is nowadays applied to all kinds of magical rituals. Modern urban style hoodoo and voodoo practice tend to make heavy use of premade formulas for working their magic. Sometimes the practitioner may create the mixture his or herself, but it's common to buy readymade magick items as well.