Luger from Killzone.
While she is relegated to the position of "token female", and the only female soldier in the series Luger is certainly the most rounded character, whose training as a Shadow Marshal means she is one of the two characters who actually consider the use of tactics instead of relying on their emotions and luck to keep them alive. Luger spends the entire game, barring cutscenes when her face is visible, in a figure-hugging bodysuit and yet is never exploited for cheesecake or in any way played to be a sex symbol. Despite being trained to be emotionally dead she brings an element of civility absent from the frontline soldiers to the game and is able to rekindle her ability to socialise on friendly terms.
The thing I like the most about Luger is that she actually volunteered for military service when it appears that she had seemingly been left behind to wait for the troops to return from war. While no other women are shown to have been willing to enter frontline service for the ISA, Luger was willing to sacrifice her life and her relationship to serve what she believed to be a just cause.