I love maps, and I especially love well-designed interactive maps that include different layers of information.  Chronas definitely fits the bill.  Students can zoom into various areas on the map and adjust the time period of the map and watch as political boundaries change.  There are also icons on the map that indicate important people, artifacts, cities,  and battles that link to articles giving more information on these topics.  You can also toggle the boundaries on the map to indicate rulers, culture, religion or population for the delineated areas.  The data at the earliest years of the map is fairly European-centric, so make sure to inform students about the cultures present in other regions.

Website: http://chronas.org/history
Subject: Social Studies, History, Geography
Grade Level: 2-12
Price: Free, but a Kickstarter campaign is planned for early May