Bryant offers an intriguing Mashup this week: The Lensman series
What the Lensman series is to me are psionicists (two rival groups), secret societies, and long term plans between two long-lived races, using their pawns and allies as the main combatants.
Somehow, I think you can do this in a fantasy (D20 if you insist) setting.
On one side, the evil Eddorians. In a fantasy world, the premier antagonist psionicists are none other than the Mind Flayers. So they are on one side, manipulating their pawns, advancing their alien goals.
On the other side, the Arisians, we’ll throw in a set of psionic dragons.
Well, like the Mind Flayers, we need something non-human with goals which are their own. Even if they are protagonists, they should be somewhat different than the PCs. And Dragons are far more likely to work through intermediaries, or disguised, than other choices.
The Dragons and Mind Flayers have been working for thousands of years against each other, subtly, carefully, influencing the civilizations of humans and the other humanoid races. This would be a large game-long campaign arc, with the PC party slowly growing into psionic talents of their own, and slowly becoming aware of the overreaching conflict.