The extremely useful Romantic Circles site at the University of Maryland has this chronology of Byron's life and times. Keep track of Byron's endless poems, love affairs, scandals and financial difficulties with this handy timeline!
This site is a treasure trove of Byron-related documents, including online excerpts from his letters, poems, biographies and criticism of his works. There are some interesting finds in here, like the gossipy book that Harriet Beecher Stowe (yes, of Uncle Tom's Cabin) wrote about Byron's marriage to her friend Annabella Milbanke.
The website of the Poetry Foundation serves as an online encyclopedia of all things poetic. The entry on Lord Byron contains his biography, links to his poetry and a bibliography of suggested further reading.
This online resource has an entry on Byron that contains a succinct biography, plus links to his poems and related readings. You can also click on a "Brief Guide to Romanticism" that serves as a helpful introduction to Byron's literary and cultural era.
The Keats-Shelley House is a house in Rome near a spot frequented by Byron's contemporaries Percy Bysshe Shelley, John Keats and other Romantic poets. Today the house is a museum dedicated to the work of the Romantics. Its website has biographies of the Romantics, including Lord Byron.