Game coding

/frog/, I'm writing a 3D game and I need help with the logic.  I'm trying to model the ability to walk around anywhere on earth.  In order to do this (& keep it interesting), I need a map generator.  I have the temptation to model it after minecraft's block generator, but I don't want to have a blockly terrain.  It should be regular terrain, like Elder Scrolls or Halo.  Does anyone have an idea about how I would do this?

tl;dr: how do I make a normal map generator?

http://freespace.virgin.net/hugo.elias/models/m_perlin.htm

I used this to generate a heightmap. It was simple, but pretty effective for basic terrain.

Of course, even if the hills are smooth and sufficiently distributed, that's not really how the world works. You won't get sheer cliffs and caves and so on.