Originality is overrated, I say. Stand atop the shoulders of greats and take the ideas of others even farther!
My favorite idea that I've stolen is from a post in another thread I started where someone explained a great way to run sandbox campaigns. Establish the existence of time and have 3 or 4 plotlines occurring simultaneously. Have each plot advance whether the PCs interact with it or not. An individual plotline could reach a critical point where the PCs have even more compelling reasons to resolve it. Or it could be resolved by other heroes who got there before you. Or whatever. Just seemed like a great way to maintain that openness of a sandbox, where players can go and do what they'd like, but add some urgency and verisimilitude that this is an actual world that moves without you.
What's your favorite idea that you've taken, perhaps reworked a little and added to your game? As a player or game master.