Michelle Rodriguez wears Mosley Tribes Raynes or Ray-Ban 3044 small Aviator sunglasses in the movie Avatar.

She plays a pilot, so these aviators are very appropriate. They are basically the same as the regular Aviators but smaller.

The Mosley Tribes Raynes can be found on Amazon for $235.00 or at Zappos.com for $279. The Ray-Ban 3044 ($72.00 - $98.95) can be found on Amazon, Frames Direct and BestBuyEyeglasses.

Reference: Mosley Tribes Raynes / Ray-Ban 3044 Arista frame Chrystal Gray lens (L0207)