I can't believe I'm saying this, but y'all can keep the Na'vi. My pick for the most impressive recent achievement in on-screen creature design is the Subsiders -- the gross, bat-like human-turned-vampire-turned abominations featured in the Spierig Brothers' fairly terrific dystopian fantasy Daybreakers.
This photo doesn't do the Subsiders justice, and their backstory (largely spoiler-free, if you haven't yet seen the film) is actually important to what makes them so profoundly creepy. The basic idea is this: In a world ruled by a civilized breed of vampire, humans are hunted and harvested for blood. Even so, the supply of human blood is running out, and shortages become widespread. If a vampire doesn't get enough human blood, he or she slowly begins to undergo a transformation from their essentially humanoid state to the primitive, brutish, barely sentient creature you now see before you. Predictably, the blood shortages affect the poorest strata of society first and worst, creating an underclass of Subsiders that the rest of the vampire world considers a menace.
Early in the film, our protagonist -- a vampire scientist (Ethan Hawke) searching for a substitute to human blood that may permit the human species to repopulate -- has a run-in with a Subsider, in his kitchen. With the exception of one sequence in Ti West's The House of the Devil, I found this scene more unsettling than anything I saw in 2009.