to correct perspective while minimizing distortion of an off-center object:
rename background layer to unlock
make new top layer
place both layers into a group
with the top layer active, make a circle selection and stroke it with color that contrasts with image
move the circle over area of image that you want to minimize distortion
Make the Group active
Place guide lines near objects that you wish to make vertical or horizontal
Select the Free Transform tool and with the Ctrl (Command) key push and pull the corners until objects are straightened while keeping the stroked "circle" as round as possible.
When finished, ungroup and delete the reference circle layer and guides

forum discussion: http://forums.dpreview.com/forums/read.asp?forum=1006&message=26591034