How to stitch several photos into a single one using Mac OS X in 360 mode or simple?
I found Hugin to be the best free alternative to PhotoSynth. I only used the Windows version but they have Mac builds too.

PTgui is a commercial alternative to Hugin using the same core library. I remember giving it a spin and not being impressed over Hugin.

Another commercial alternative is Autopano (started as a free GUI to panorama tools and went beyond that with PRO and Giga versions). I has a more polished look and feel and the Giga version is targeted at really large panoramas (think 26 gigapx).