Smarty - Smarty provides address validation, autocomplete, geocoding and reverse geocoding services covering addresses in over 240+ countries.
ClickToAddress - ClickToAddress offers APIs for address lookup and verification.
Addressy - Addressy is address verification software that captures and verifies addresses on websites.
Experian Address Verification API - Experian provides Address Verification API for accurate, complete USPS addresses with minimal data entry.
streetlayer - Free, international and secure address validation, autocomplete and geocode JSON API for developers and businesses - compatible with PHP, Python, and more.
AddressFinder.com.au - Start enjoying accurate address data, all the time.