The Amazing Website of Shakespeare's Sonnets
http://www.shakespeares-sonnets.com
Named appropriately, this site really is amazing. Here you can find the full text of Shakespeare's sonnets, each accompanied by an in-depth summary and line-by-line analysis. You can also see how the sonnets were written in the original 1609 Quarto and read a modern paraphrasing if you are having trouble with Shakespeare's English.
Hudson Shakespeare Company: Sonnets
http://www.hudsonshakespeare.org/Shakespeare%20Library/Poetry/sonnets.htm
This site features commentary on the sonnets and argues in favor of identifying the fair lord, dark lady, and rival poet as Henry Wriothesley, Emilia Bassano Lanier, and Christopher Marlowe, respectively. A good introduction to the kinds of discourse used in scholarly attempts to unlock the mysteries of these elusive figures.
Shakespeare's Dark Lady
http://www.shakespearesdarklady.com
Plenty of websites claim to show definitive proof of the identities of one of more of the unnamed characters in Shakespeare's sonnets. This one is rather unique: it explores the identity of the dark lady, here argued to be Lady Penelope Rich, in fictional narrative form. The entire novel is available on the website.
Enter Willie Hughes as Juliet
http://www.infopt.demon.co.uk/shakespe.htm
This website argues the case for Willie Hughes as the fair lord's real-world counterpart. Although this view is not prevalent, the site does feature an excellent discussion of the homoerotic undertones in Shakespeare's sonnets.
The Rival Poet of Shakespeare's Sonnets
http://www.geocities.com/Athens/Troy/4081/RivalPoet.html
This site puts forth George Chapman as the rival poet, referencing Chapman's own works as reflected in the sonnets.
Some Interesting Mathematical Facts about Marlowe's Sonnets
http://www2.localaccess.com/marlowe/sonnets.htm
Yes, this website is mistitled. But those with an interest in possible Shakespearean numerology might want to check this out. Although perhaps not the most reliable of sources, it provides an interesting read.
Sonnet Central
All you ever wanted to know about the sonnet and then some. This site is a one-stop source for learning about this centuries-old art form. Find examples of sonnets from across time and around the world, as well as guidance for writing your own.
Wikipedia: William Shakespeare
http://en.wikipedia.org/wiki/Shakespeare
Available in multiple languages, this Wikipedia page offers a solid starting point for research into Shakespeare's life and works. It also offers a good selection of links to other useful web-based resources.
Open Source Shakespeare
http://www.opensourceshakespeare.org
Did you enjoy the sonnets? Want to read more Shakespeare? This open source site provides full texts for all of Shakespeare's works, as well as some handy search tools.