Something else to add to The Infinite Download List Of Infinite Downloads is Aether, a major mod for good ol' Minecraft that's so fat with features and changes that you could almost call it a total conversion. It's also an extension of Minecraft's ill-defined, open-to-interpretation fictional universe. If The Nether is Minecraft's hell, then Aether is its heaven - an even more abstract cube-world of floating sky-islands, angry birds (no, not those ones), loot-holding dungeons and flying whales.
They had me at 'flying whales.' Oh, and there's a ton of new block types (including trampoline-like bouncy clouds) plus an expanded, more RPG-like accessory system and even difficulty tiers for the new dungeon runs.
This one will require full exploration for a longer, later post, but meantime find out more and get it installed here.
Bit of a bastard to install, requiring a few other mini-mods first, so if you're struggling or not in place where you can download lots of random zip files, here's The Yogcast's exporation of The Aether: