I have a used truck with dirty carpet. I'm looking for a good carpet shampoo that can be had farely easy. The leather has a few spots on it as well, but that's another story.
If you're looking for something quick and OTC, the Blue Coral Carpet/Upholstery Shampoo can be found at most K-mart/Walmarts. It does a decent job unless you've got ground in stains.