US Zip code databases

I am working on a little app that requires a good zip code database.

Any idea where can I find the best zip code database, that is up to date and also can be updated if needed?


Do a Google search for “us zip code database”, and the ads above and to the right of the search results will be full of sites that can sell you that database. It’s not too expensive.

there seem to be tons of different ones. Any experience which ones are the best ones to use?