The VIES Validate VAT Number PHP SDK by PH7 validates EU VAT registration numbers against the central ec.europa.eu database using the official Europa API. It uses real-time data feeds that could be useful in online payment forms according to the author, avoiding fraud with expired or wrong VAT numbers.
ValueAppeal is a service to help U.S. homeowners appeal the assessed value of their home. Over-assessed property results in taxes that are higher than they should be. This means that homeowners may be over-paying their taxes by anywhere from $500 to $1,000 or more. I wouldn’t mind keeping an extra $1,000 of my money per year going forward and I bet the same goes for most of America. If you have a website focused on real estate (did anyone mention this to Zillow?) the ValueAppeal API could augment it with compelling information.