My favorite SDK sample is under \Graphics and Multimedia\Animation and Timing\Animation Composition sample.  First off, it has a super elegant but very powerful transform that animates a panel to a very cool effect that mimics 3D in a 2D space.  Secondly, it gets into the mind twisting topic of composing animations -- mashing two animations together to create new effects.  The composition of time: heady stuff.  More on this next in a future post...