In reviewing the data from geonames, I discovered in my spot check that Indonesia is missing. A bit of time with Google revealed a few places where I could buy data sets but nothing open.

Anywhere where this data is known to be available free of restrictions?

Edit: It looks like there are a few countries missing. Singapore is another one that is missing. There may be others. I would assume the Singapore postal system can manage if a zipcode is omitted but not sure about other places.