Canon has a pretty good program called Image Stitch or something like that. I think it's free for download at their site too.

I've used it a few times and it does a fairly decent job, to my untrained eye. It'll take multiple images (I've done up to 4) arraigned in various order (line or grid) and combine them like you're asking about. It also did color and brightness balancing good enough that I couldn't detect a difference even though two photos I used once were slightly off of each other (I think I accidentally turned the polarizer at some point). This was for a landscape panoramic.

Huh, I’m finding all the other software other that that one… go figure.

[edited to typo a correct]