Courtesy of David Weinberger, here’s a profoundly-ugly website that provides in-depth commentary for each of Shakespeare’s sonnets (plus a bunch of other poets):
All the sonnets are provided here, with descriptive commentary attached to each one, giving explanations of difficult and unfamiliar words and phrases, and with a full analysis of any special problems of interpretation which arise. Follow the instructions below to find your way around. Sonnets by other Elizabethan poets are also included, Spenser, Sidney, Drayton and a few other minor authors.
Proceed with caution, as the site is an offense to web designers everywhere (do you bite you thumb at me, sir?). It could be a spectacular site, if the information was totally re-organized.
DarrenBarefoot.com 
‘Tis indeed a “crusty botch of nature.” (Troilus and Cressida) Very concise, however.
Insult courtesy of the “Shakespeare Insulter”
http://www.pangloss.com/seidel/Shaker.
Did I say concise? Nevermind. It’s the labyrinth from HELL. Still trying to find something positive to say. If I’m not out in 24 hours, someone call the paramedics.