Good quality maps can help students understand complex concepts and interactive maps are even better for allowing students to dig deep and make connections in a way that makes sense to them.  ArcGIS maps are not only visually stunning, they contain a wealth of data.  Available maps range from historical empires around the world to 911 calls in the Boston area.  Maps can be viewed for free, or paid users can create their own map layers.

If you’re into more interesting historical maps, the CIA has just declassified decades’ worth of maps that can be seen here.

Website: http://www.arcgis.com/home/gallery.html
Subject: Social Studies, Geography, History
Grade Level: 4-12
Price: Free to view maps, plans start at $500/year for five users and decrease in price for more users