Modelling Techniques

Are you referring to ways of creating models, or ways of drawing models?

If you're talking about creating models:
I can not remember what it's called right now, but there is a method of modeling that works like so:

1. Start with a shape, usually a block.
   
2. Alter the positions of the vertices.
   
3. Extrude one or more faces of the shape a certain distance, or along a curve.
   
4. Go to step 2, until the model is finshed.
   

It's good for things like trees - objects with lots of protrusions and whatnot, although it could really be used to model anything.

Also, if you are indeed referring to the creation of models, you might want to try posting in one of the art-related forums. You'd probably get better answers there.

I mean ways of programming surfaces which are combined to create models?

I have made a deformable NURBS cube, now I'm wondering howto program a NURBS sphere, any1 know?

From a rendering perspektive subdivision and poligonal modeling have no difference. They both produce triangle (or quad) meshes.

As far as I can tell, there are only two ways of representig a surface. Explisitly givig the verticles for some kind of geometric shape and implicitly difining them through some sort of mathematical function. Nurbs are implicit, poligonal models are explicit.

You might be interested in metaballs (an other kind of implicit surfaces), though.