Wolfram Research
Wolfram Math World: Rational Number
This site gives an overview of rational numbers, gives interesting facts about the rational numbers including countability and probability of a rational numbers denominator being even. The site also contains related links.
Math Words
Math Words: Rational Numbers
Mathwords provides a brief description with an easy to read chart that includes all types of real numbers.
Education Place
Houghton Mifflin: Eduplace: Lesson Plan: What Is It? Rational Numbers
This site is a great place for lesson information on the concept of rational numbers. Three other tabs are available besides the-What Is It? tab. They are Tips and Tricks, When Students Ask, and Lesson Ideas. Each tab has just the right...
Wikimedia
Wikipedia: Rational Numbers
Learn the definition of rational numbers. You can also look at some examples and properties, plus learn about Egyptian fractions. Links are provided for additional information.