Bucyruss' BiomeTerrain Mod is a modification for Minecraft that lets you fiddle with Minecraft's world generation algorithms- anything from biome size and type to custom trees. Now, that's probably worth a post in itself, but far more entertaining is this playful competition over on the official Minecraft forums where people are battling to create and post the best settings to use with that mod. I've made a gallery of the best ones below, and I'm going to try my hand at some VVVVVV-style naming. Above, we have Zarkauff's Continental Rift, or what I like to call "Wet Tiers of Sorrow".
Here's Reikos' Sky Gardens, or "I Hope You Brought a Change Of Trousers".
RiverC's Victoriox, or "We Are Not All Created Equal".
Zarkauff's Times of Sand, or "Dune Bugger".
Kourru's Euphoria, or "Do Not Drink And Dick Around With World-Generation Code".
Atreyu's Eroded Monsoonal Plains, or "Idiot Savannah."
formlesstree4's Underworld, or "Argh".
And finally Rushen's The Oceans Blue, or "Settler's Lament".
For a closer look at any of these beauties (or to get the code that generated them so you can use them yourself) (OR to take part in the voting), here's the link to that forum thread again.