Centers for Disease Control and Prevention
Centers for Disease Control: Atsdr: Toxicological Profile for Benzene
Benzen is an aromatic hydrocarbon that has been found to be a carcinogenic (cancer causing) material. Possible routes of exposure, effects on helth, medical tests to determine exposure, and recommended levels of exposure are detailed.
York University
York University: Benzene
This site from York University gives detailed information on the structure of benzene, including mentioning August Kekule, who discovered the correct structure.
Columbia University
Intensive Organic Chemistry: Arenes and Aromaticity
Lecture notes from Chapter on Arenes & Aromaticity. Can be downloaded using Adobe Acrobat.