The (London) Times has created a searchable archive of every issue published between 1785 and 1985. It includes scans of 20 million articles, pictures and ads and you can save, print, or email articles. Also included are letters to the editor by Thomas Hardy, Queen Victoria, Oscar Wilde and Charles Darwin.
The ads alone constitute a great social history, and the births, deaths and obituary pages also reflect the conditions of the times, from the French Revolution to the Falklands War (more recent issues will be added later).
It should come with a warning sign: Danger, abandon all hope of getting your work done, ye who enter here! The temptations to browse and dart from topic to topic are extreme...but what fun for any history buff--or just someone who wants to know what was happening in the world on the day they were born.
Of course for writers it's priceless--and, for the moment, free. Just register and the world is your oyster.
(For tips on writing fiction and non-fiction, see www.timetowrite.com and also www.yourwritingcoach.com and my book, "Your Writing Coach," published by Nicholas Brealey.)