This site has a definition and properties of Leptons, the "Basic building blocks of matter." There are links to table of properties and more information.

The beginning of an informative tutorial on antimatter, covering quarks, hadrons, baryons, mesons, leptons, and neutrinos.

This site defines hadrons and their characteristics. There are links to explanations and more detailed information about interactions and composition.

This particle physics tutorial discusses the different types of leptons: the electron, tau lepton, muon lepton, and neutrinos.

An introduction to the Standard Model, a theory which attempts to explain atomic structure using leptons, quarks, and force carrier particles.