What are some great Quartz 2D drawing tutorials?

I devoted an entire class to Quartz 2D drawing last semester in my advanced iPhone development course. The video for that is available on iTunes U, along with the rest of the class. The course notes for that session can be found here, and I created a sample application to show off some more advanced Quartz drawing concepts.

Beyond that, I highly recommend reading the Quartz 2D Programming Guide.

Start with Apple's Quartz2D demo project. Compile it, run it on your device, read the code while you use the demos in the app.