Take a look at this Silverlight 4 tutorial written by Vibor Cipan about using PathListBox with Expression Blend 4.
Sample Data has been available to us from Expression Blend 3, but now with Blend 4, Silverlight 4 and Expression Blend 4 SDK there is new control – PathListBox enabling you to create list box looking however you want them to look – not just rectangular. This allows you to create nice radial, spiral and many other types of layout.