There's a better set of tools than using Windows Presentation Foundation (WPF) straight out of the box: WPF plus Prism (formerly "Composite Application Guidance for WPF and Silverlight") and Unity. Prism focuses on letting you turn your XAML file into a true view, supported by a completely separate ViewModel class.
Because your XAML view is built declaratively, you might have blunders in it (incorrect property settings, for instance), but you can't have logic errors. Instead, your bugs are limited to your procedural code (the validation code, the integration with your business objects, workflow management and so on), which is segregated into your ViewModel class. That ViewModel class can be developed in parallel to your view and, more importantly, built using test-driven development (TDD) to ensure it works correctly. Once your view model is built, it just needs to be wired up to your XAML to create your application.
Unity focuses on giving you runtime flexibility in that "wiring up" phase by providing the ability to create composable applications -- applications that choose their parts at runtime. Instead of hardcoding class names into your code, you specify the criteria for the classes you want to use. At runtime, your application looks for the class it needs and loads it. This gives you an easier way to swap in and out your views and view models from one site to another, from one scenario to another (premium customers versus ordinary customers) or from one state to another (test versus production; supporting a customer in default versus supporting a customer in good standing). Applications determine the criteria for the components they need by reading a configuration file or by making decisions based on information in the environment.
It's a different way of thinking: Using Prism and Unity with WPF is as much about adopting a way of creating your applications as it is about adopting new technology. And while I'm focusing on WPF in this article, Prism and Unity work equally well with Silverlight, throwing in the ability to dynamically search for the classes to download to the client as a bonus.
The easiest way to get the Prism/Unity combo is to use the Extensions Manager on the Visual Studio Tools menu to search for and install the NuGet Package Manager. Once you have NuGet installed, you can right-click on your project and select Manage NuGet Packages. A search in the online forums on Prism will bring you to the Prism.UnityExtensions package, which you can download and install into your project.
Been a while since I've highlighted a Prism/Unity post or article. I've been hearing Prism/Unity noises around me so wanted to grab this for future sharing/etc. Plus I thought it cool that we're seeing this a few days early (the article post date is 7/1/2012 and today is 6/27/2012). Finally I just liked the depth and detail...