This tool from Microsoft called Image Composite Editor lately caught my attention. It is a free panorama sticher that does not need any information about the camera specs and the order of the images. Just drag your photographs taken from a single camera location to create a high-resolution panorama incorporating all the source images at full resolution. This is the easiest to use stitching software I’ve ever used.

I use it a lot for site photography but it’s a great tool too for stiching high resolution maps captured from the web (like in this tutorial on Digital Urban)
A nice feature is that it will export to multiple formats including JPG, TIFF, Photoshop, HD View Tileset, Deep Zoom Tileset, Windows Bitmap, PNG, and HD Photo Image. And you can export layers if the format supports it (for example, Photoshop) to help with additional post-processing.

State-of-the-art stitching algorithms automaticaly place source images and determine panorama type
Advanced orientation adjustment view allows planar, cylindrical, and spherical projections
Support for different types of camera motion
Excellent exposure blending using Microsoft Research fast Poisson algorithm
Automatic cropping to maximum image area
No image size limitation – stitch gigapixel panoramas
Native support for 64-bit operating systems such as 64-bit Vista
Output in a wide variety of image formats:
HD View
Silverlight Deep Zoom
TIFF, JPEG, PNG, and more

Microsoft Image Composite Editor is provided free of charge and without official support. However, if you have questions or issues with Image Composite Editor, you may find help at the Image Composite Editor Forum, which is monitored by the developers and provides community-based support.