I am not a professional developer, and while my day job involves a lot of scripting, I don't have a great deal of experience with software architecture. Design patterns are tough to grasp without context, and the examples provided with many online tutorials esoteric to the point of making things worse.
Not so with this little gem. I was delighted to discover that I was doing MVC right; idem for the observer pattern.
This page is by no means complete and it's not as detailed as some other tutorials out there, but what it lacks in depth, it more than compensates for with clarity. For those new to design patterns, this is well-worth the read.