After playing around with a few photo stitching programs, I've finally settled on Hugin (which dtasker demonstrated for me last week). It is free and open source, and available for a wide range of computer platforms. The version I'm using includes a wide range of options, including automatic and manual modes (ie, let it do everything automatically, or manually pick out the points you want to match up from each photo yourself), exposure and white balance adjustment.
It also has a choice of which method(s) to use for fusing/blending the photos.
The manual methods are a bit fiddly, and and take some getting used to. I haven't really got the hang of it yet (way too many options for me to bother figuring out what they all do), but here's a simple two photo panorama I put together from a couple of shots I had handy...