University of St. Andrews (UK)
University of St. Andrews: Cissoid of Diocles
Detailed and comprehensive site explaining the Cissoid of Diocles. A Java-enhanced interactive is included.
Wolfram Research
Wolfram Math World: Cissoid of Diocles Pedal Curve
Short site explaining the Cissoid of Diocles Pedal Curve. The site has links to related topics, and includes a graph and a brief explanation.