Correcting Lens Aberrations in Digital Photography?

Kavau asks: "I've recently entered the world of digital photography, and bought a pocket-sized digital. While the resolution and the color accuracy are very nice, I was utterly disappointed by the (lack of) quality of the zoom lens: It has a clearly visible barrel distortion, especially in wide angle, so that straight lines appear curved in the picture. This is especially annoying in architectural shots or cityscapes. While grumbling about this shortcoming, I suddenly realized that I am dealing with digital imaging here: In principle it should be no problem to measure the distortion, and then to correct it with a digital mapping. Other lens faults such as vignetting could also be corrected. Now, since I don't want to reinvent the wheel, here is my question to Slashdot: Do you know of any open-source tools that deal with issues such as (1) applying general analytic transformations to a picture, (2) specifically correcting for barrel distortion, or (3) determining the amount of distortion from test pictures? Also, since people probably had this idea before, does anyone have experience with this issue that he/she wants to share, or some resources to point out?"