jonathanwkelly/ups-shipping-rate (packagist): This is a very simple class that uses the UPS web service to get a shipping rate. Basically, you pass it the shipping method you'd like to use, the destination / shipper zip codes, the package dimensions, and receive a shipping quote. There are plenty of values that are hard-coded in the XML request that could be passed in dynamically for a more robust rating process.
Keywords: api|shipping|ups|Rate