I see quite often (maybe because I am searching for it) people recommending Geonames for postal code data, etc. I've taken data from Geonames and a few other places and spent some time cleaning it up. I found that quite a bit of the data in Geonames is outdated/incorrect. So far I've only done this for the United States, but I'd like to share my data. I was thinking about adding an answer to each question where someone mentions Geonames, but that seems like a long process. Any ideas?