Hi,
I have tried this small bit of freeware tool out from Microsoft Research and while it is designed for stitching together panoramas it has a poor to decent chance of stitching together centerfold or other magazine scans automatically in a few seconds. The resulting file can be saved and it should look as good as your source material.
System Requirements
Operating system: 64-bit version of Windows XP, Windows Vista, or Windows 7
I assume it will work on Windows 8.
The biggest bug I have found (detailed below) is when the drag and drop functionality doesn't work and I have to use the manual mode.
----->
Structured Panorama dialog sometimes shows diagonally-striped boxes instead of thumbnail images.
Depending on the aspect ratio of your photos, the thumbnail images displayed by the Structured Panorama dialog may get corrupted, showing lots of diagonal stripes instead of the actual images. This is a bug in ICE, and it will be fixed in our next release. Note that the incorrect thumbnails have no effect on the final stitched output, but they certainly make the Structured Panorama dialog hard to use. (For now, you may be able to avoid the problem by rotating your images 90 degrees or cropping them a bit before bringing them into ICE.)
----->
I recommend this for the times when it just works and I have posted some before and after pictures. Not all are awesome, but it is free...
Paint.net 
Stitched 
Left Mag Page - Right Mag Page ----- Stitched --------------- Paint.net ------ Stitched
The Paint.net images were done by me before I got this cool software tool.
Cheers!