I'm a doctor, not a mechanic
Legacy:Nvidia Texture Tools
The NVIDIA Texture Tools are a collection of useful texture manipulation tools.
Photoshop DDS Plugin
This plugin allowes Adobe Photoshop and other applications that can use Photoshop-compatible plugins to open and save .DDS files. The download for this plugin also contains one for creating "normal maps" from height map bitmaps, which might be interesting for modding games based on the third generation Unreal Engine.
3D Studio Max DDS Plugins
These plugins allow 3D Studio Max to read .DDS files. The download includes plugins for 3D Studio Max 3, 4 and 5, as well as source code for the latest version.