The US News Map has taken digitized newspapers from 38 states and compiled them into a fantastic tool for historical studies.  Students can input a search term and a range of dates and then animate the map to see instances of that term in newspapers articles from those years across the country.  When available, students can also navigate directly to the original image or transcript of the newspapers in question.
Website: http://usnewsmap.com/
Subject: History and Social Studies
Grade Level: 3-12
Price: Free