Post your favorite, and why its your favorite.
By non-causally related fantasy worlds, I mean, if your favorite fantasy world is Tekumel, choose another. Tekumel is explicitly stated as thousands of years in our future, where humans survived an apocalyptic war, rebuilt society and technology, went into space, met aliens, colonized the world of Tekumel, and then the Tekumel system fell into a dimensional anomaly whereby they were able to contact powerful extradimensional beings and work magic, but they could not see the stars anymore.
So Forgotten realms is OK, Greyhawk is OK, Dragonlance if OK, Middle Earth is not. Hawkmoon is not.
Hopefully this will inspire me to do something Space Opera-y, something where the inhabitants of (whatever fictional world) Farasat, for example (randomly grabbed a book off my desk and pointed to a word and it was my Farsi dictionary and the word means Sagacity), go out into space and get involved in some conflict.