These GIS "Lite" tools are web-based and allow for a quick map that you can share on the web. A great starting point.
These GIS "Medium" tools are a little more advanced but require little training. These tools provide added sharing ability like web apps, access to data, and data manipulation abilities.
These are full-fledged GIS desktop applications --the sky is the limit. I recommend these to GIS students, advanced users, and those who need to conduct some form of spatial analysis on their data.