I am not a fan of MS. But check this out: http://msdn.microsoft.com/en-us/library/ff859477.aspx
RESTful Location Service API does not seem to post any restriction.
You can user Find Location By Point API: http://msdn.microsoft.com/en-us/library/ff701710.aspx
I tried out the sample for geoNames, the result is not good enough for me as I need county information, and the response time is slow.