What software has made you go "wow?"
listic: Second Reality, in particular, the Mandelbrot fractal zooming part. Realtime Mandelbrot zooming, in 1993, on a 486
 - this really made me go "wow", if you know what I mean.
Then it was that Globe zooming thing in 3DMark, don't remember which one - it should impress casual observe more, but I was not so impresed - I know that modern 3D card and CPU should be able to handle it.
Afterwards, it was Google Earth that made me go this kind of "wow"