To celebrate the 150th anniversary, my colleague at the University of Birmingham, Barbara Bordalejo, working with John van Wyhe at Darwin Online, has produced a fantastic new digital online variorum, which is much more flexible and user-friendly than Peckham's. Take a look at it here: http://darwin-online.org.uk/Variorum/index.html
For more details, see the editor's introduction: http://darwin-online.org.uk/Variorum/Introduction.html
At last, all of us can follow the evolution of The Origin!