Aligning Vertices

I wonder how you can align selected vertices in a model to the x-, y- or z-as.
There is an option in the uv/image editor, i thought it was called align x/y, but i cant find a similair option for modelling.

Cheers,

Leichim

Select vertices to align, hit s, press axis (x, y or z), press zero (0) and confirm with enter.