I really liked the xaml transition themes in Windows 8. They give a nice way to have consistent animations from within your application and through application to application.
One transition theme I really like in Xaml was the entrance theme. One feature of this theme is it has an “IsStaggeringEnabled” in which it will stagger the animations of items within the same container, giving an incremental loading effect.
I wanted to use this effect in WPF and here it is. I also added a few more features for controlling the animation that Win8 Xaml doesn’t include (and for good reason).
Please note that virtualization of things like ListBox can cause the effect to go overboard, so you may want to use: VirtualizingPanel.VirtualizationMode=Recycling attached property.