I have a recipe for Dutch apple raisin cake that calls for a half teaspoon of allspice, which I don't have. Would ground cloves or nutmeg or a combo of both work? I know that allspice is a spice unto itself.
The closest thing is to combine equal parts of ground cinnamon, cloves, nutmeg, and black pepper.
Hobodave's suggestion is good. Also, you could just choose any combination of the classic "sweet" spices and be content with making something slightly different than the original recipe but not necessarily better or worse. Don't be a recipe slave!