How about some Post-Apocalypse/Fantasy crossover?
Not just "WWIII/The Super-Plague/The BIG Asteroid/etc. came, destroyed civilization but brough the magic back", but rather this:
A high fantasy world, filled to the brim with sentient races, glorious empires, elven forests, dwarven mines, evil liches and shining heroes is destroyed in some global, probably magical, disaster. Now the ragged survivors, many of them thrown back to bronze age technology at best, crawl from the ruins to re-discover a world full of ruined cities, magical mutants, weird cults, and mysterious artifacts. The old gods don't answer prayers anymore, the elves have vanished or mutated, dragons are just legends now or have changed into something unrecognizeable, and magic as a science is almost completely lost...