In the pursuit and development of malware detection algorithms, often a big sample set of both malicious and benign samples is required. Both machine learning or similar automated techniques, as well as manual or partially manual signature generation, often require a good and varied example set of benign samples that are commonly mistaken as malicious.
Those samples are usually being automatically analyzed and then provided to a Reverse Engineer for further scrutiny, analysis and improvement of said malware detection algorithm.
Although finding malicious samples is frequently discussed (see multiple questions), discussion about benign sample sources seems lacking.
What are good benign sample repositories/feeds, preferably focused on potential/frequent false positive samples? Other sources or "retrival methods" (scraping) are also welcome!