Can anyone recommend a language, library, framework or book which focuses on GUI programming from the perspective of a web developer?
I have experience in web development, for example HTML/AJAX/PHP/MySQL among similar technologies. However, I have never programmed my own back-end, or any kind of standalone program. Does anyone have experience making this transition, and what would I best study to help make the leap from the browser to creating programs with GUIs (primarily for Windows)?
Have a look at Windows Presentation Foundation (WPF). It's GUIs are built with XAML, which is a language very similar to HTML.
You could also have a look at Adobe FLEX or Microsoft Silverlight, which you can use to build desktop applications.
I made the transition from client/server applications to web development. The biggest single difference that took some getting used to was the loss of state. Since the web is stateless, but desktop applications are stateful, client applications have many more interaction and interface options easily available.
The best things to study would be some straightforward desktop application frameworks. For Windows you'd probably want to start reading tutorials focused on .Net desktop applications. Start with simple walkthroughs that you can try yourself to get a feel for what you'll be getting into.
In the short term, you could use Appcelerator Titanium to create desktops (or mobile) apps using the web technologies you already know. Pretty cool stuff, IMHO.
Assuming you are experienced from MVC design pattern, swing supports this pretty well:
http://www.javaworld.com/jw-04-1998/jw-04-howto.html
In particular you can use the spring framework with java desktop applications and have swing be the front end: