The Shakespeare Authorship Page
A pretty thorough refutation of the Oxfordian (and Baconian) (and Marlovian) claims to have written the Shakespeare plays.
The Oxford Shakespeare Society
A society dedicated to proving that Shakespeare's plays were actually written by Edmund de Vere, 17th Earl of Oxford. There's a beginners' guide to the authorship debate which is well worth a look if you know nothing about it, whilst the rest of the site goes into great detail. Not directly relevant to theatre, of course, but interesting nonetheless.
The Shakespeare Mystery
A very thorough site, relating to a US PBS TV Frontline programme on the Shakespeare authorship debate. The "Oxfordians" and the "Stratfordians" each have their say in the Update section; there are seven full articles on the debate itself; there is a reading list (pretty comprehensive!), as well as reactions to the broadcast - some of them severely critical about the programme's balance.
The Writing's on the Wall for Shakespeare
A 1992 article from the Evening Standard "proving" that Bacon wrote Shakespeare's plays.