The British Library has digitized various versions (quartos) of Shakespeare's plays and made them available on its web site so you can compare the quartos. There are 93 copies of the 21 plays. The twenty-one of Shakespeare's plays were published in quarto before 1642. Using the site, you can view two versions side-by-side, page-by-page.
This is a wonderful use of digitized items! It gives to scholars and non-scholars alike something that is useful (and fun). Students reading Shakespeare in school might use this site to research a paper, while people who are just interested in Shakespeare might like looking at the graphics used in the various quartos. It is also interesting to see -- from a web design point of view -- how the British Library presents the quartos, and what additional information they make available for users.