Three community-made patches for Thief 3. Together they unlock native-resolution widescreen and all manner of smaller visual tweaks.
ALL OF THESE PROGRAMS NEED WRITE ACCESS TO THE T:DS FOLDER. In Windows Vista or later, right-click and select "Run as administrator".
Installer for T:DS Tweaker, which can apply various visual and aural tweaks to the game like making text smaller and reducing/eliminating the blue "interactive object" glow.
Patcher that unlocks widescreen field of view settings. See the link below for setting widescreen resolutions.
A patcher that fixes the game freezing on exit and when loading a saved game when running widescreen. You may or may not need this.