"Charles Harrington Elster - Verbal Advantage" is the best option if you really want to increase your vocabulary. Browse it on net, you will get so many resources to get benefit from his work. I am also working on vocabulary now a days and it has proved to be a belssing for me.
You can download it or buy a cd of it. In fact listening to his vocabulary programmes is the best option as one can get the exact pronunciation of it.
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