<p>Marriam-Webster[/url</a>], [url=<a href="http://www.wordsmith.org/awad/sub.html%5DWordSmith%5B/url">http://www.wordsmith.org/awad/sub.html]WordSmith[/url</a>], [url=<a href="http://signup.dictionary.com/wordoftheday%5DDictionary.com%5B/url">http://signup.dictionary.com/wordoftheday]Dictionary.com[/url</a>], and [url=<a href="http://www.oed.com/services/email-wotd.html%5DThe">http://www.oed.com/services/email-wotd.html]The</a> Oxford English Dictionary all have word of the day services (though none of them is specifically for the SAT or standardized test prep)</p>
<p>The</a> New York Times also has a "Word of the Day" from words in recent news stories, though I don't think they have an email service - you'll have to check the website</p>