So, a big mod called The Aether has been released that basically takes the concept of the Nether and inverts it. We get a bunch of floating islands, several new enemies, three types of dungeons, rare items, accessories, rings, pendants, and mounts that fly.
I have NEVER used a mod before, so setting up the Aether was a chore... but totally worth it. My portal gated right into a bronze dungeon... which had like 5 more immediately nearby. I've done almost all of them, hauling out a ton of Zanite Swords, Flaming Swords, and Phoenix Bows. I hope to find a silver soon, but I die waaaay too much for my tastes (even on easy). The poison Moas especially take me out quite well. I haven't fallen off the islands yet, but I figure it's just a matter of time
Anyway, I highly recommend it. IMO, this is what Notch should have been working on for the past few months. There's also a handy video in the forum post for newbies like me to install the mod.