All CS3, no plug-ins:
I corrected the image the best that I could with the Lens correction filter, adjusting both perspective and distortion. This exposed voids in the lower corners and greatly distorted the top of the leaning tower, but it does a good job of getting the overall proportions right.
I used the Transform warp tool to reshape the tower and filled the voids that were created by using the clone tool.
I cloned in the lower right corner to fill the void and used a portion of the building to fill the void in the lower left.

forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=30736002&changemode=1
original image by Bob Burasco: