I've used (and continue to use):
1. Calico
2. Hugin
3. DoubleTake
4. The "panorama" feature of Photoshop Elements 6

What I find is that none of these work well with all of my panos. Each program seems to hiccup on a different kind of issue. By having several in my hip pocket, I can almost always get a decent stitch with one of these.

DoubleTake is among the easiest to use of all of these. When it works, it's very fast and very effective.