The first logical substitution for a whole vanilla bean is pure vanilla extract. Two to three teaspoons of pure vanilla extract is equal to one vanilla bean.
Vanilla powder is a suitable substitution for custards and other desserts because it lacks the alcohol contained in vanilla extract. Substitute two teaspoons of vanilla powder for one vanilla bean.
Vanilla sugar is simply granulated sugar infused with vanilla flavor. Replace one vanilla bean with one to two teaspoons of vanilla sugar. Because this alternative is sugar-based, cut back a bit on the sugar required in a recipe.
Substituting almond extract in place of the vanilla bean is an option, but this slightly alters the flavor and outcome of a recipe by giving a robust, nutty background in place of vanilla flavor.