procedural terrain generating

any good tutorials about procedural terrain generating /prog/? I am currently particularly interested how rivers can be generating, how do the affect the terrain.

I'd say just look for more efficient ways of getting the information you want to be created.

You can look at procedural vs pseudorandom vs random, usually there's not a clear distinction with the first two in terms of dynamic content.

Completely unrelated (but I'm thinking of it for some reason), the way Valve does their lettering and spray/label/sign texturing is actually very inventive, like they use two 32x32 images to come up with sharp high-resolution vector images.

Also maxes are an interesting bit to look at if you're into that stuff, as well as cellular automata.