Go to https://adwords.google.com/select/KeywordToolExternal, perform a search, download the CSV file, then paste it in to the box below.
The system will discard any keywords that have a local search volume of 40000 or more, to help concentrate on finding untapped keywords (assumption being that if there's more than 40000 searches on it, it's possibly too popular already to get in under the radar).
The system will then determine how many pages are in Google for the given keyword, and finally determine a score to help you easily see potentially untapped keywords to target. Higher scores would generally be considered 'better' targets when looking for a keyword to dominate in the search engines.
Currently the system will only work on up to the first 15 keywords at a time while this is in testing mode.
Feedback to mgkimsal@gmail.com please