Try Kekus's
Calico, or get
Autostitch (the original codebase for Calico is Autostitch) and run it via Parallels on the Mac. Calico runs rings around Canon's Photostitch.
10x3 (30 photo) stitch:
If you're feeling ambitious (and you want free software), you can also try the PanoramaTools open-source frontend,
Hugin, but that kind of powertool is most suited if you're doing 360°x180° pano stitching.