Using Pano [app store link] I got better matched skies today, and sharper alignment. The blend between the two images was good, and once you do a rough align, Pano takes care of the rest. At US$2.99 it is the bargain of the offerings.
TripStitch [app store link] gave me an acceptable image, but it was a lot of trouble because you can't take the image from within TripStitch. You have to go out to the iPhone camera app, then import the images into TripStitch, which I feel is an unnecessary step. I also didn't see any auto-alignment feature, so it's all up to the photographer. TripStitch is US$4.99.
Panolabs Pro [app store link] gave me a lot of control, but an image that I felt was below the quality of the others. I tried on several scenes, but manipulating the images for a smooth merge is difficult, and the controls are not fine grained enough to make delicate adjustments. I've shared my best effort with you in the gallery. The app is US$4.99.
Panorama did a nice job as well. It was pretty easy to merge and align the images, and the final result looks pretty good. It was the most expensive app of the group, but it was not head and shoulders above Pano or TripStitch. It allows a lot of control and lets you select the final resolution for saving. It does a nice job of guiding you through the process of taking and aligning the images.
So there you have it. A look at the options for making panoramic shots from the iPhone. Of course, you can get better results using a higher resolution digital camera, and something like Adobe Photoshop or Elements or 3rd party apps like DoubleTake or The Panorama Factory to stitch them all together. It is remarkable, though, that you can get decent pano photos from what is arguably a less than top-quality cellphone camera.
Click on the gallery below to see the images produced by the apps.