I do use PostgreSQL wherever possibly. Add http://postgrest.com/ and nginx as a url-rewriting proxy and you have a performant, highly adaptable REST-Server.
Nice, Postgrest looks really amazing, especially for long-term production needs. I've previously used Sandman, which is much easier to set up, which makes it ideal for more quick-and-dirty needs: https://github.com/jeffknupp/sandman2