There have been several posts in which the question was raised about converging parallels, the phenomenon of buildings ‘falling away’. This happens when a tall object such as a building is shot from ground height. Our brains compensate, but our cameras don’t have our capacity for self-deception.

There are several workarounds, my favourite being a tilt-shift (Canon) or perspective control (Nikon) lens, which unfortunately is the most expensive (and requires extensive practice with manual focusing and a tripod). A wide-angle lens will usually exaggerate the effect, but captures more and allows you to sacrifice more pixels in post-processing.

Image-editing software allows some control over converging parallels. In Photoshop, there are three main approaches:
1) Tick the perspective option in the crop feature and adjust the markers. I find this the least subtle method which often significantly distorts your images
2) The Filter > Distort > Lens correction function has several controls which can be used – sparingly! – for correction
3) The completely manual approach: select your image and then Edit > Transform > Distort and pull the markers. It’s best to display a grid to help you, but ultimately it remains a pure guestimate, which is half the fun
I usually try a combination of all three depending on the extent of the distortion.
There are also dedicated applications. One such is DxO optics which offers a convenient perspective correction feature.
Below are some examples using the same image along with screen captures of the software mentioned above.
Hope this helps.

The RAW capture straight out of the camera


Screen capture of DxO PC with its before and after screens


[imghttp://img36.imageshack.us/img36/1716/cp03.jpg[/img]