I highly recommend the MelissaData.com web services for address verification:
<a href="http://www.melissadata.com/dqt/websmart-global.htm" rel="nofollow">http://www.melissadata.com/dqt/websmart-global.htm</a><p>One single web service that can validate addresses for just about every industrialized country.<p>Also, if you are interested in seeing example "correct" addresses for many countries, see Address Doctor.
<a href="http://www.addressdoctor.com/en/countries_data/countries5.asp" rel="nofollow">http://www.addressdoctor.com/en/countries_data/countries5.as...</a><p>Both of these companies are leaders in their field.
This makes a lot of sense.<p>However, I'm growing wary of "dependency sprawl", where the functionality of a web application is tied to an increasing number of other services. That said, as far as uptime goes Google is hard to beat.
I agree, this is very useful. Entering address information into separate fields is something we have, sadly, come to accept. From a user standpoint though, this makes no sense. I write my address on an envelope, and the US post office delivers it just fine. Why would I need to separate my address?<p>One thing to keep inmind is the Geocoding limit. If this is used on a busy website, you'll need to build in checks:<p><a href="http://code.google.com/apis/maps/faq.html#geocoder_limit" rel="nofollow">http://code.google.com/apis/maps/faq.html#geocoder_limit</a>
Major problem with this approach is that textarea doesn't have an autocomplete feature. Having single line textboxes for each field allows me to tap the down arrow and have previous entries listed. With a multiline textbox I have to manually type all my information in.
Also... really only works for the US only. Canada is not half bad but Google returns an invalid postal code (due to licensing restrictions or some such). Outside of US/Canada accuracy falls way off to the point of being almost useless.
I hacked up one of the first address validation services on the Internet: <a href="http://www.cedar.buffalo.edu/adserv.html" rel="nofollow">http://www.cedar.buffalo.edu/adserv.html</a> , back in 1998(?).<p>I've since moved on, and the backend database hasn't been updated in nearly a decade. But it works fairly well, and can take free-form addresses as input.<p>I'm surprised there aren't more such free services out there.
Sorry to comment spam, but, Yahoo has a "PlaceFinder" API that does geocoding (and address cleanup): <a href="http://developer.yahoo.com/geo/placefinder/" rel="nofollow">http://developer.yahoo.com/geo/placefinder/</a>