Wikimedia
Wikipedia: Electronegativity
This encyclopedia article from Wikipedia gives a definition for what electronegativity is, information on the two scales of electronegativity that are in common use (Pauling and Mulliken Scales), and a discussion on electronegativity...
Other
Chemguide: Electronegativity
This page explains what electronegativity is, and how and why it varies around the Periodic Table. It looks at the way that electronegativity differences affect bond type and explains what is meant by polar bonds and polar molecules.
Upper Canada District School Board
Tom Stretton's Chemistry Pages: Ionization Potential and Electronegativity
Deepen your understanding of ionization potential and electronegativity in this illustrated presentation.