World of Ruin from FFVI is always something I like, heh.
But I think Distant Tower is perhaps my second favorite. I'd have to come up with some sort of tower for the game, though, but that's not too hard -- there just isn't some singular tower at the moment.
Not that it would be hard to add, because of the build/level editor and all that jazz. I'm sure there will be towers either way (well already there are small ones), but it's a matter of whether or not those will have some key story significance.