On Architecture - Text of the English-language translation of 1826 by Joseph Gwilt, as well as a French translation and the Latin text (Teubner 1899 edition), hosted by Bill Thayer in his Lacus Curtius site.
Plates from Cesariano's Edition of Vitruvius - Woodblock illustrations were added to Vitruvius's text in the edition published by Cesare Cesariano (Como 1521). Images from Art Serve at the Australian National University.
Vitruvius - Comment on Vitruvius's work by John H. Leinard of the University of Houston's College of Engineering.
Vitruvius (c. 70-25 BC) - Very brief biography of the author of the earliest surviving treatise on architecture - 'De architectura' (On Architecture) - from Eric Weisstein's Treasure Troves of Science.
Vitruvius, On Architecture - 12 plates from an 18th-century Venetian edition, hosted by the University of Pennsylvania.
Vitruvius Pollio, The Ten Books on Architecture - The full text of the English translation by Morris Hicky Morgan (1914), hosted by the Perseus Project. Easy navigation through the text; map of sites mentioned.
Vitruvius: 1st Century BC Roman Architect - Brief biography and outline of the contents of his famous work 'De architectura' from HyperHistory Online.