Rudi Grobler has released a pack of WPF themes for you to use to make your applications convey the atmosphere you want to convey. Applying them is as simple as one line of code in your application as a whole, or window-by-window, or you can do it in XAML. Rudi's blog tells how. It really makes a difference to the mood of your application and lets you stand out from the crowd.
I shrank the images because people object when the chrome on the right gets messed up by big images. You can see the originals on Rudi's blog - I just want you to see how very different the same application looks when you change themes. BTW, these themes were originally released for Silverlight and Rudi converted them for WPF. Pretty slick!