For Prospero, his library was dukedom enough. I verified this through a search of The Tempest on Google Book Search just now. Many readers will have seen that Google Book Search has a Shakespeare page:
This summer we’re working to make Shakespeare even more accessible with our website at www.google.com/shakespeare, where you can find and search through all of Shakespeare’s plays, from familiar favorites like Hamlet to more obscure gems like Troilus and Cressida. The site launches in conjunction with our sponsorship of Shakespeare in the Park, New York’s wonderful outdoor festival, which this summer will feature a production of Macbeth. [Inside Google Book Search: No holds Bard]
The entry says that they will be working on the site over the summer, and I am sure that additional functionality will be added. It is a strangely flat debut given the range of higher level services they are so well-placed to offer. This seems especially so given recent discussions about the research potential of having computational access to masses of textual materials (see the D-Lib article by Gregory Crane, for example).