General Reference: Quotation Sources

• A Short Dictionary of Scientific Quotations
  For example, Archimedes (ca. 235 bc)
  Concerning levers: "Give me a place to stand, and I will move the Earth."
• Bartlett's Quotations
  This tenth edition of 1919 contains over 11,000 searchable quotations and was the first new edition of John Bartlett’s corpus to be published after his death in 1905. (from the site)
• The Quotation Page
  You've reached the oldest quotation site on the Web, established 1994. We have over 26,000 quotations online from over 3,100 authors, and more are added daily. (from the site)

When ... and how ... to use quotation marks.