Sam Elliot is a good choice, a good actor that could do Druss very well.
My fav would be though Oliver Reed, he was a great actor and looks like he was the real Druss
The voice was also very commanding, a voice i imagine Druss must have. Very shame he is dead. He died too young only 60.
Look at the pic in the link !!
http://www.geocities.com/movias/gladiator.jpg