Notch just posted a video of his hard work on biomes. I must say, I am very satisfied. If Notch released the update with only biomes, I'd be happy. But of course there will be much more. Notch and his team have outdone themselves. Check this out!
Biomes. They’re not final yet, but this is about how they will be in the Halloween update.
Monster spawning and terrain features can be tied to individual biomes, so some biomes could get special trees, or special mobs, or different grass, to make them all more unique.
These are the biomes. Try to spot them all from this picture: