If you attended the session Nakul and I did on the ArcGIS for Local & State Government Solutions or the ArcGIS Online Steps for Success session, here are the links to the Model Organizations I showed in the demonstrations. These downloads include some nice looking thumbnails, icons, and other graphics you can use for your own items and groups in your local or state agency's mapping portal. I use the PowerPoint template all the time to create my own "tweaked" thumbnails. I have access to SnagIt as well and use that as a tool to create images in combination with the thumbnails in these PowerPoint resources. Thanks to the Solutions team for these great resources!
Remember one of those best practices steps: building a good brand and clean design on your item thumbnails, including meaningful descriptions and tags, etc. will help you achieve success with one of those challenges Chris left you with to light up your Organization with geography and maps!
ArcGIS Online for Local Government Model Organization download
ArcGIS Online for State Government download
ArcGIS Online for Emergency Management download
ArcGIS Online for Water Utilities download