Visit http://modeling.3dreview.com/bobo/ipas/ELLIPS.HTM and download the plug-in.It lets you "morph" between Cube,Sphere,Cylinder,Octahedron and some special variations of these...Actually you have only to change some parameters, it is much more easier than morphing.You can, of course, create a Sphere and a Cube using Super Ellipsoid and use as morphing targets, but animating the settings is the better way...Look at the animated gifs on the page, they show how it works...