"Positioning" by Ries and Trout: <a href="http://www.amazon.com/Positioning-Battle-Your-Al-Ries/dp/0071373586" rel="nofollow">http://www.amazon.com/Positioning-Battle-Your-Al-Ries/dp/007...</a><p>It was THE marketing book of the 80s, and it's still extremely relevant today.  It's quick read, too.