Microsoft has released an update to its Image Composite Editor (ICE), which is an “advanced” panoramic image stitcher.  I have used this to create some panoramas of images I have taken, and I will say it does a remarkable job at stitching them together.  This update includes several new improvements, including the ability to upload images to Photosynth.

New in v1.3.3:

• Accelerated stitching on multiple CPU cores
• Ability to publish, view, and share panoramas on the Photosynth web site
• Support for "structured panoramas" — panoramas consisting of hundreds of photos taken in a rectangular grid of rows and columns (usually by a robotic device like the GigaPan tripod heads)
• No image size limitation — stitch gigapixel panoramas
• Support for input images with 8 or 16 bits per component

More information and downloads can be found at http://research.microsoft.com/en-us/um/redmond/groups/ivm/ice/.