Canon image files come with a .CR2 extension. This is new to me. To import these into gimp, install gimp-ufraw (Unidentified Flying Raw, built on DCRaw).
I've only used it once, but it looks like it adds a entire import function to gimp that, once you select the .CR2 file to import, or any other raw camera image file it supports (seems to be a huge list here), you get a tiny little program with way more options than I imagiend would be necessary. Very cool.
