An app like Barcode Scanner but for resistor color codes: Using the camera (and probably requiring the flash), read the color bars off a resistor and output the resistance value.
I have little doubt that it’s possible, but at the same time, it’s probably a nontrivial problem in image processing and pattern matching. And, beyond its niftiness factor, it’s not something that very many people would pay for. So, not worth the effort, unfortunately.
It’s more the sort of thing that some geeky Googler should do in his 20% time. Or, some random geek with more time on his hands than me.