I've just started reading d20 Modern, WotC's latest d20 offering, and it seems like it may work well for an "Archetypal Hero" campaign. The basis of this idea is the comic book series Mage by Matt Wagner. For those who haven't read the series, it concerns incarnations of various heroes of folktales, myths, and legends, appearing in the modern world to continue the fight against Evil. Each incarnation has the spirit and general powers associated with the hero -- for example, the incarnation of "The Olympian" has the legendary prowess of Heracles, and also happens to be burdened with 12 labors; the incarnation of Coyote is quick, tricky, and skillful -- but the incarnations are still real people with regular lives, until something happens to awaken them to their role. The heroes are defenders of humanity and the Light, fighting against various supernatural, mythological monsters that prey upon people, and the agents of the Dark. Behind the scenes, the Umbra Sprite seeks to find the Fisher King, an agent of goodness who if sacrificed will give the Dark great power, plunging mankind into a period of darkness and misery. In turn, the heroes of the Light have the guidance of Mirth, the World-Mage and titular character of the series. Some heroes have unique weapons associated with them, though the form may be different than in the legend -- a sword may now appear to be a baseball bat, for example -- while other heroes have all their power within. The heroes also may cooperate, or they may develop rivalries and compete to see who can get the most monsters -- perhaps losing sight of the true goal, the defeat of the Dark. Generally, the public are unaware of the heroes, their monstrous foes, and the war, but sometimes the heroes do have to find ways to work around the public without their knowing.
The d20 Modern rules provide six basic character classes, each associated with one ability score -- the Strong Hero, the Fast Hero, the Smart Hero, and so forth -- so it is already geared toward an archetypal game. However, the classes are obviously geared towards multi-classing (there are only 10 levels for each, and the class abilities are fairly generic and basic), and the default "Advanced" classes are written for a generic modern setting. Very probably each hero would need a custom-designed "Advanced" class to match his (or her) incarnation, but many of the powers are common enough (immune to mundane weapons, for example, or super-fast) that existing spells could be re-written as Feats and used as special abilities for the Advanced Hero class to use. This can be a fun way for players to play their favorite hero from myth or legend, while having the freedom to put their own spin on the characters.