I have posted before about Navizon
, the iPhone pseudo-GPS system. It uses cell phone towers to provide a rough estimate of your location without using actual satellite GPS positioning information. It costs $25 to buy and people have reported mixed results. Since all the cell phone tower information is provided by volunteers, some positioning is more accurate, especially in areas with a high population density where people have better filled in data.
If you don't mind being off by a half mile or more, Navizon has released a low-rent freebie version that they say is accurate to about 1000 meters. (Navizon claims 10-30m accuracy for the paid version.) This makes the tool pretty much worthless for anyone, say, on the Amazing Race (they took two clues, why weren't they penalized?) but not so bad if it works for people driving along highways.
Download a copy from Installer.app.