Might as well make a flip side to the other thread. Most people on this list will probably fit the stereotype of the "character actor", AKA "the guys/women who do not possess enough sex appeal for the 16-35 age crowd and thus will never be the lead in a studio project." For those types, the first two that pop into my head would be Stephen Root and Stephen Rea.
For people who are regularly highly billed actors, I would go with Ralph Fiennes. He had prominent roles in two of my 10 favorite movies of the last decade (the Constant Gardener and In Bruges) while playing almost polar opposite characters between the two.