Tutor2u
Tutor2u: Income Elasticity of Demand
This site provides a detailed study of income elasticity, which is how one's demand changes as income changes. It also gives good examples of normal and inferior goods.
Wikimedia
Wikipedia: Inferior Good
Offers a description of an inferior good, and uses an Indifference Curve to illustrate how an increase in income will cause a person to demand less of a good.