These are a few projects which I thought were interesting; the asset tracking application is one which I have developed more than once for different customers. The other two are based on questions I saw on a my SQL discussion list. I felt compelled to write more than the typical answer (a snippet a code and a few pointers) because it's seen these brought up interesting problems. All available here, hopefully the be of use to someone.
Spockproxy is a fork from MySQL Proxy that is designed to shard data. This was developed and is used by us at Spock.com. These are the slides from a talk I gave about the proxy; why shard data, how to make it work, what it does and does not do well.
Asset tracking This is a full-blown LAMP application designed to track hardware assets. This was primarily intended for the folks who work in data centers or who do desktop support and need to track computer equipment. It also has facilities to track people, purchase orders and to create special reports.
B&B reservation system This is an article detailing a very simple LAMP application which shows rooms available on a specific date for date range and allows the user to make a reservation. The application itself is very plain but it show some interesting techniques such as dealing with dates, calling functions to create your page and searching for data that is not there (show all the rooms without reservations).
The Period Table The basic question here was how to show an average over time (the table in question had start and stop dates). This technique is one of my favorites because you crate a Cartesian product on purpose so that you're able to count the daily totals an aggregate on them.