Hugin
So you are off on vacation on the gulf of mexico, you take a series of pictures by standing in one place and snapping pictures as you move horizontally, now you want to put them together to make a panoramic image. How to do it?
Hugin is a free download from Sourceforge.net that will stich the images together based on common images in each picture.
I strongly recommend using the assistant tab as it makes melook smarter than I am :)
Hugin version for Windows