Due to the fact that this result is still common on Google when searching for Geocoding API alternatives to Google due to License, I figured I would answer as well to provide more clarity.
Google Maps and most mapping providers that offer geocoding will not allow this type of usage or any usage really that doesn't involve directly using their Mapping Products.
There are other APIs specifically for this purpose. To name a few:
I'm sure I've missed quite a bit here, but those are ones I can think of immediately that allow you to use them without mapping requirements.
If you are doing USA only, there is also the US Census TIGER/Line Geocoder.