Maple syrup and almond extract are good substitutes for vanilla in a recipe. Both ingredients have a similar flavor and consistency to vanilla, and the difference is hardly noticeable.
Ingredients that give a strong vanilla flavor are vanilla milk, vanilla beans and vanilla paste. Rum or brandy can be good vanilla substitutes if the cook doesn't mind adding alcohol to the recipe. Some cooks use Fiori di Sicilia as an alcohol-free vanilla substitute.
Each vanilla substitute has a slightly different flavor. If more than one substitute is available, the cook can sample each one and see which flavor she prefers.