Aerial View Maps

What are good freeware GIS OS and map sources?

I want to work with free downloaded maps and aerial photos and edit them in a GIS. What are the best GIS software? What are best GIS OS (or do software come bundled with an OS?) What are best sources of maps and aerial photos for USA? thanks

Public Comments

1. I think this website should give you what you want!
2. There are a lot of places to get data - ESRI provides a great (very powerful) software, Its not cheap - but they do have free downloadable viewers and data. Check out their sites here - Viewer - http://www.esri.com/software/arcgis/explorer/index.html Data - http://resources.esri.com/arcgisonlineservices/