Ask HN: How best to make use of Amazon Web Services free usage tier?

I'm thinking of signing up to use Amazon's Web Services. I have created and hosted simple websites (static HTML, Wordpress blogs etc) before on shared hosting plans, but I'd like to learn more indepth stuff, such as running a VPS or creating a simple web app. What projects should I experiment with to make the most of the AWS 12-month free usage tier?