Google News has added a cool and useful new feature. Google News Archive Search lets you search more than 200 years of historical newspaper archives. When you do an archive search, links in the left-hand pane let you narrow your search by date or by publication. Resulting pages are either HTML or PDFs of scanned newpaper/magazine pages; some of the results are free, link to paid newspaper archives.
This is a great way to do historical research -- another great addition to the suite of search features offered by Google. Check it out!