I have been trying to find an easy way to compute sales tax in states like Washington that have multiple tax jurisdictions. The manual sales tax plugin could possibly work (albeit a bit of a maintenance chore) if I could just specify "ZipPlus4" type zip codes in the formulas. The problem being that nobody knows or enters their Zip+4 zip code. I found a nice service that will verify addresses (with type-ahead support) that could work great, but they only offer plug-ins for "other" eCommerce sites, and not for nopCommerce. (See www.addressy.com for a simple demo).
It uses a simple javascript code that needs to be in the header of the page that asks for addresses.
What would it take to incorporate that script into a plugin to allow type-ahead address validation, such as is shown in the demo, for Zip+4 resolution so you could apply the correct tax calculations as well as assuring a valid shipping address?