In my opinion, Dream Theater. I love almost everthing they've done but The Astonishing is their masterpiece to me.
Other possible contenders would be Cradle of Filth, Anathema, David Gilmour, Roger Waters (taking his last album to be Amused To Death, not 'Ca Ira'), Marilyn Manson, and (contraversial but I love 10,000 Days) Tool.