Microsoft Research Image Composite Editor
This free utility that runs on 32 and 64 bit machines has no size limits for image compositing. Although the site says that multiple point perspectives are not currently supported, a geographer from the French equivalent of the USGS says that he has used it to do a multiple view mosaic. The code is NOT opensource, but this could save time IF a community decides that they need the data quickly.
The tool is here: http://research.microsoft.com/en-us/um/redmond/groups/ivm/ice/
If anyone has experience with this, please post as there is nothing on the googlegroup with Microsoft's ICE. I will try this and post results as soon as I get back to the US to a computer with some data sets on it.