Forget about those pre-built one shot solutions as their picture quality is really bad. (already tried them).
There is one solution that is perfect but it is very expensive and you'll have to build it yourself.
It involves:
3 cameras, 3 lenses, 3 tripod heads, a base plate, and a custom 3 way wired remote control. You can buy the setup listed below or you can build it yourself from scratch. The 60 degree tilt is not necessary if you are using a wide fisheye. This setting will take the zenith fully, and leave a very little nadir blindspot which you can photograph later.
http://www.agnos.com/prodotti.htm?v…corafotoprodbig
The baseplate and the tripod heads
http://www.agnos.com/foto.htm?imgfo…orrp_00_big.jpg
The remote control
http://www.agnos.com/foto.htm?imgfo…none_00_big.jpg
Eventually you will have a setup close to this: (without the protruding sticks and wires).
http://pencil-jp.net/weblog/data/061112/mrotatorr_01_ing.gif
I was about to build it but the shipping cost from italy for the plate was too high, and my camera supplier wasnt able to deliver on 3 used cameras which he had promised etc... so i didnt try it, however i found some websites that had tried it successfully. Let me know if you need more info.