SF world concepts:
Dragons and dragon riders: Honestly I still haven't seen a version of this which really does well at the "dragons are people too" part. The originators are Dungeons and Dragons and Anne McCaffrey's Pern series, though.
Humans converted into computer-like minds controlling spaceship or mecha bodies: Anne McCaffrey's Ship series, some Transformers fanfiction about humans being converted into transformers.
Shinigami and Personified/Soul Weapons: Soul Eater and Bleach; Utena is a slightly more distant ancestor.
Connection between aliens and Earth's ancient history (alien archeology): Stargate
Concept of possessing another human combined with time travel: Quantum Leap
Labyrinth of spiritual tests: Jim Henson's Labyrinth
Some of my favorite world-concepts are hard to tie to a specific origin. For example, I like shapeshifters who can take any form and have to consciously build themselves into the form they want to take, rather than shapeshifters who have some magical affinity with some type of animal. But other than Odo from ST Deep Space Nine, I can't recall any good examples of this type of shapeshifting.
Edited by sunandshadow, 13 November 2012 - 05:29 PM.
Phone game idea available free to someone who will develop it (Alphadoku game - the only existing phone game of this type is both for windows phone only and awful. PM for details.)
I want to help design a "sandpark" MMO. Optional interactive story with quests and deeply characterized NPCs, plus sandbox elements like player-craftable housing and lots of other crafting. If you are starting a design of this type, please PM me. I also love pet-breeding games.