I am very impressed with Google\’s recent launch of its News Archives Search. Basically, in partnership with major content owners, Google is indexing newspaper and magazine articles going back to the 18th century.
I spent an hour doing various searches and found the content very interesting, although a lot of the historic newspaper content is full of typos and OCR errors, and much of the best content is available only for a fee. Over time, more and more good historical content will be free. The Time Magazine content is very useful.