I found this mod and i would rly rly rly LOVE it to see something like this on bukkit !!!! I know this must hard to do but i think when someone can make THIS possible, he will earn more money than anyone before with a plugin xD Lg Mega
http://forums.bukkit.org/threads/increased-map-height-128-test-plugin.47786/ Spoutcraft already has this feature for single player, they are planning to develop a plugin for multiplayer as well. I too am looking forward to it.