For the purposes of a series of blog posts on EntityFieldQuery, I've created a simple module that demonstrates some uses of EntityFieldQuery.
Some quick notes about what the module contains: the module installs three node types, efq_article, efq_page, and efq_photo. These are very simple node types: efq_article and efq_page each contain a body field for text, while efq_photo contains a single image field. In addition, all three content types contain a US States field, which we'll be using to construct some example queries.
Additionally, the module defines a menu callback that uses EntityFieldQuery to generate a listing of these content types that is filterable by state and by node type arguments. It also defines a block which lists other content in the system that matches the state of a given node, if such content exists.
I recommend using Devel content generate to quickly generate content for your examples, although you can of course create it manually if you like. For the purposes of my examples, I created 200 nodes using the following command: drush genc --types="efq_page,efq_article,efq_photo" 200.
When you uninstall this module, it will clean up after itself, removing all created content. I'm thinking of teaching this technique to my cats.