Pretty sure it's a Speedlite 580 EX II:
http://www.warehouseexpress.com/product/default.aspx?sku=1017952
http://www.warehouseexpress.com/product/default.aspx?sku=1017952
Nice one, Cliff.
How much does it weigh, and what's the minimum speed you can hand-hold it at? Looks great, but your dog looks a bit bored.