This site serves as kind of an online Keats fan club. It is chock full of letters, poems and facts about the poet. The nifty thing about this website is that it's actually designed to be viewed over your mobile phone. Now you can read Keats' poetry while tapping at your phone and pretending that you're popular.
The University of North Carolina created this website when their acquisition of Keats' works brought the total number of books in their library to six million. It is a great overview of the poets' life, with a concise biography and insightful analysis on Keats' legacy.
A Keats fan named Marilee has maintained this comprehensive website of all things Keats since 1997. It has lots of cool primary documents, like Keats' letters, poems and manuscript pages.
The British Library's online encyclopedia has a nice multimedia entry on Keats. It contains a brief biography with links to some of his best-known poems and essays analyzing his literary impact.
The boarding house in Rome's Piazza di Spagna where John Keats died is now a museum. Today the house is a museum dedicated to the work of the Romantic poets who stayed there. Its website has biographies of the Romantics, including Keats.
This website from the University of Maryland is a great introduction to Romantic literature. Many of the Romantic poets lived together, worked together and hooked up with each other. You can't study one without getting caught up in the others.