CodePoint Open has been freely available for a number of years. It doesn't include delivery endpoints but for geolocating English, Scottish and Welsh (but, alas, not Northern Irish) postcodes it's fine.

http://www.ordnancesurvey.co.uk/business-and-government/prod...

Unfortunately we lost the postcode database as a public asset in 2013 when the UK government sold off Royal Mail[0], despite the database being compiled at huge cost to the tax payer.

This is a real shame as people had to campaign for years before the data was made freely available to begin with.[1]

Hopefully though, as long as the government still holds a large stake, we'll at least have Code Point. The Royal Mail also offer some developer options[2]

[0] http://www.bbc.co.uk/news/business-26605375

[1] http://www.theguardian.com/technology/2009/jul/22/free-our-d...

[2] http://www.poweredbypaf.com/developer/

Host it in the US, there is no database copyright in the US.

Actually, zip codes are proprietary business information of the USPS. Which is why ZipLocate uses ZCTA codes (similar, but based on data collected from censuses).