A student just recently showed me this one and I was blown away. (Thanks J.D.!) CG Society put together this great article on a VFX-intensive Snickers commercial produced by BBDO Moscow, Sky Films in Toronto, and a German post facility called Unexpected. The article includes some great info about how they produced the spot, including fantastic breakdowns of the various elements - live action, CG layers, particle systems - that went into each shot.
Read the full story here.