Dig this: Quartos.org!
The Guardian explains:
Funded by the UK Joint Information Systems Committee and the US National Endowment for the Humanities, the Shakespeare Quartos Archive (www.quartos.org) is a free resource that will in time reproduce at least one copy of every edition of Shakespeare's plays printed in quarto before the theatres were closed by the Puritan parliament in 1642.Yes, that means you can compare line by line the famous "bad" quarto of Hamlet to all other editions. For instance see if you spot anything, er, odd in the bottom left monologue below:
Currently, there are 32 copies of Hamlet available to view – all contributed by the project's partner institutions, which own the majority of pre-1642 quartos: the Bodleian, the British Library, the University of Edinburgh Library, the Folger Shakespeare Library, the Huntingdon Library and the National Library of Scotland.
The website offers far more than just a photographic reproduction of these rare texts. [...] Features that would be impossible to replicate even by traipsing off to university libraries all over the world include the facility to overlay a speech from one edition on top of the same speech from another.
Yes, those immortal words: To be, or not to be, I there's the point!
Lost forever is the Dramaturg's script note: "Lovely solil., Will. But might not Hamlet say "question" instead? Always questing, better journey, thinkst thou not?"