I was a bit surprised that Liara wasn't the internet's girl of choice. The Asari exhibit much more sexuality than the Quarians (they are obviously Mass Effect's version of the Twi'leks), and unlike Tali, Liara actually is a romance option for both male and female Shepard.
I suppose it's partly because Liara is a traditional scholar while Tali is a techie, and the internet prefers techies above all. Also, Tali is more mysterious, what with the mask and all.
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Yoblazer: http://i32.tinypic.com/zlf1w7.gif
Watch and you'll see... someday I'll be... part of your world!