The Math League
The Math League: Decimals, Whole Numbers and Exponents
This tutorial has definitions and examples of decimals, whole numbers, and exponents. In addition, a variety of topics are covered, such as comparing, multiplying and subtracting.
Lawrence Hall of Science
The Math Page: Skill in Arithmetic: The Meaning of Decimals
This website from The Math Page explains and defines decimals.
Help Algebra
Help algebra.com: Decimals
Keeping in mind that decimals are really fractions, this site shows you how to convert decimals and work with them in solving equations.