Wolfram Research
Wolfram Math World: Golden Ratio
Math World explains the Golden Ratio, gives the formula for finding the irrational number, and expresses this value as an infinite series. Also defines and represents the Ratio geometrically, its relationship to the Fibonacci numbers,...
Other
Mathematics: Fibonacci Numbers and the Golden Section
This resource contains everything you ever needed to know about Fibonacci numbers. You'll find mathematical and historical facts, examples, problems, interactive demonstrations, and more.
University of Chicago
University of Chicago: The Golden Ratio Activities
Many activities for the classroom involving the golden ratio.