I've got Zach Randolph near the top of my list. He recently signed a big contract, has always struggled with conditioning and motivation.
I don't know why Randolph keeps getting put on this list. He's always been in good shape and was known as a gym rat from my recollection in Portland, even with his many faults.
He's been a problem off the court and defensively, but never because he's not in good shape.