[cft]

I was turned off by their blurp that their US zip codes database contains only 21k zips out of 41.5k. Are they sufficiently complete for small towns?

[hamandcheese]

The incomplete zips (for at least one database I've read about) come from corporate or industrial areas where not many people actually live.

[maxerickson]

Officially US zip codes are just collections of addresses, they don't necessarily correspond to areas.

I think most free datasets are probably just the areas that Census derived for TIGER (or at the very least, rely heavily on that data).