I used to use Autostitch (http://cvlab.epfl.ch/~brown/autostitch/autostitch.html) running in WINE. When that stopped working for me, I switched to Hugin and haven't looked back. It works well, and is quite powerful. You can even use it to create lens profiles for your lenses to correct distortion. There are very useful tutorials on the Hugin website (http://hugin.sourceforge.net/tutorials/index.shtml).