I was watching the match between Vera Zvonareva and Daniela Hantuchova last night and the commentator just commented that Daniela had the longest legs in women's tennis - and the most beautiful, I might add. She's tall at 6'2 and it helps that she also plays a mean game of tennis.
Well, after Daniela, I'd have to say Maria Sharapova, also can lay claim to this title. Also at 6' herself, Maria is also playing very well at the moment and yes, takes advantage of that legs of hers. Interestingly, both women are also good movers in the court, despite of their height.