As the beta of Tom's Pannini perspective correction software has timed out,
and while I am waiting to hear from him, I have been trying the latest CS6
Wide-Angle Perspective filter.
I've been able to make presentable images, suitable for printing and free
from curves that "should" be straight, of some of my equirectangular 2:1
images, with aspect ratios of 16:9 and higher (in one case 2.5:1). The
angular coverage actually reached 360 degrees in one case! I don't think
that even Pannini can achieve that...
My wife was quite impressed that something looking so "like a normal
photograph" could be printed rather than having to be viewed on a computer.
Try it, you may like it. Not all panos are equally suitable for this tool
(or maybe, as is more than likely, I haven't mastered its use yet) but
when it works it works amazingly well.