For a good introduction to Chaucer and to The Canterbury Tales see the excellent resource at Harvard University’s website, which includes a version of the text in middle English with an interlinear translation into modern English. An extensive set of links to resources for studying Chaucer can be found at the Electronic Canterbury Tales website.
There is a middle English text of The Canterbury Tales at the University of Michigan’s Corpus of Middle English Prose and Verse and also at a free private website called Librarius.
Both provide the text which was originally made available online by the Oxford Text Archive, and which is based on the Bodleian Library’s copy of The Works of Geoffrey Chaucer, edited by F. N. Robinson (London: Oxford University Press, 1957).
The digitisation of the British Library copies of the Caxton Chaucers was undertaken by the HUMI project of Keio University.
A CD-ROM edition produced by the Canterbury Tales project with additional functionality is also available from Scholarly Digital Editions.
The Caxton's Chaucer site is the outcome of one of a number of digitisation projects for early printed material held by the British Library.
The Mercers’ Company, the London guild of wholesale merchants to which Caxton belonged, is no longer a guild, but the Mercers’ Company is still in existence, and several of the documents relating to Caxton are still to be found in its archives.
Portraits of some of the persons mentioned on the British Library’s Caxton web resource can be found on the web pages of the National Portrait Gallery, for instance Edward IV, Richard III and Henry VII. You can also see a portrait of Louis de Gruuthuse who protected Edward IV when he was in Flanders. His magnificent town house still stands and is now a museum.
Information on the technique of printing can be found on several websites, for instance a resource on type making has been made for the Huntington Library.
You will also find useful information at the site of the Gutenberg Museum in Mainz, and the British Library's own web resource on Gutenberg.
On the history of papermaking, especially in England, see the British Association of Paper Historians.
The museum in the old paper mill in Basel has a short virtual tour, as does the Italian paper museum at Fabriano, which has some information on the important early Italian paper making.