Well, there ain't no "definitive" cross picking style. Bill Napier and George Shuffler are the names most Bluegrass musicians call up when "crosspicking" is discussed, and if they're a bit obscure for your blood, then Doc and Norman Blake should fit the bill.

Perhaps the most celebrated of all crosspickers is Jessie MacReynolds (on Mandolin)

Thing is, they all do it differently. Jon's description of "Down, Down, up", is how I do it anyway.

Cheers

Rick