How To Show Code Samples?
I honestly believe that 90% of the really good programmers would be able to provide this easily. A certain level of expertise can only be reached by working on your own code just for research and fun. Combine this with several years of experience, and I'm sure that you've got to have significant amounts of high quality code lying around.
Like the original poster said, it's not asking for code that was written specifically for the job application, it's asking for code that you have already written.