It was Mogwai that got me into post-rock back when I was in college. I'm still a big fan, but I sort of fell away from post-rock for a while. And I have God Is An Astronaut for bringing me back to the glorious fold.
It's hard for me to single out just one God Is An Astronaut song to recommend because they are all so damn good, but "Echoes" is as good a starting place as any. It has a typically meanderingly melodic sort of soft guitar noodling, interspersed with a rolling waves of crescendo. And then ultimately, it ends in a fucking awesome storm of screaming distortion. It's like Mogwai plus 65daysofstatic. Or something. The point is that it's damn good.