Check out my newest: http://www.carpricevault.com
It uses some custom node types to let guests enter info about car purchases or leases. You can browse the taxonomy context-driven hierarchy of makes and models and it should show summary data for models and for models in each state. The bottom of the front page shows a simple list of the most-often reviewed models (not a big list at this point). Clicking one of those will take you straight to a summary page.
You can also browse dealers, who can be associated to price reports with the old tagnode module. Each dealer's page shows a list of price reports and an embedded scrollable Yahoo map. The dealer db is still under construction.
There's a lot more theming and report building I want to do to this, but thought I'd throw it out to the community for comments...
Happy Drupal-ing !