Here are a few sample class projects (the first four are in Google Earth):
PhilaPlace is "an interactive Web site, created by the Historical Society of Pennsylvania, that connects stories to places across time in Philadelphia’s neighborhoods. ... The PhilaPlace Web site uses a multimedia format – including text, pictures, audio and video clips, and podcasts – and allows visitors to map their own stories in place and time."
The Thematic Mapping Engine allows you to create a file of UN data which can be viewed in Google Earth.
Also see the GEHacks Download page for KMZ files of cities, events and image overlays that can be displayed in Google Earth.
Google Maps includes the "My Places" tab, which allows users to drag-and-drop points onto a map and add photos, descriptions and links. Additionally, there is a "Collaborate" option to allow editing by others. All this and more is explained in their Help Guide (see also the complete list of online tutorials).
For projects requiring collaborative entry of data, you can use Spreadsheet Mapper to create layers for Google Maps or Earth. If you have a spreadsheet of locational data, you can also use Google Fusion Tables (not available with Google Apps accounts).
Some web services enable you to enter your data into a Google Map and display it on your website or create a link to it on the host's site:
If you have a large number of addresses that need to be validated, you can use Batch Geocode, which can produce a file for either Google Maps or Google Earth.
Many sites will help you to map your photos to their geographic locations; Google Maps Mania posted a comprehensive listing of these services. Great for that summer road trip!
Google Earth has a fantastic User Guide which will show you not only how to use GE but also how to create your own layers of interesting places.
Google Maps Maps, directions, satellite imagery
Google Earth Explore, search and discover ... in 3D
Google APIs The "official" Google website for building your own maps
If you are not familiar with Google Maps or what it can do, here is Getting Started with Google Maps. And here is the product tour for Google Earth.
There is actually more than one blog dedicated to Google Maps and Google Earth. Who knew?
Google Maps Mania
Google Earth Community
Google Earth Blog
Ogle Earth Blog (Google Earth and other virtual globes)
Google Lat-Long Blog
And here's a simple example:
View DHi Student Sample Locations in a larger map