I see that this software tool has not been mentioned on the forums so I will post some information about it and link from here.
For those who do not know what a DDS file is: It is a Direct Draw Surface, a DirectX image file format optimized for use in DirectX, and other engines on the Windows and console platforms. It is able to pre-process MIP maps, cube maps, indexed palletes, alpha channels with compression, volume textures etc, so that your game engine does not have to. (Unless you are using dynamic texture sources)
This Compressonator package by AMD provides one method of creating such files; primarily with compression, cube maps and MIP maps. These MIP maps for your textures are produced prior to your player loading your game, so your engine does not need to process them for you during image loading; hence the slowdown when loading lots of large textures.
If you do not know what a MIP map is, basically it is a set of textures derived from a source texture, produce in smaller scales. Instead of rendering a large texture on object in the distance, the engine will select a smaller texture in the MIP map. Rhetorically speaking, why render a texture larger than the view of the surface it is applied to?
You can already create DDS files using code, and also NVidea plugins for Photoshop, and alternative plugins for Gimp. But this AMD solution seems to have more compression features than the aforementioned solutions, and appears to be more streamline and CPU friendly; a great tool companion to say the least; plus it is free.
The compressonator also provides live image comparison windows and support for cube maps and volume textures, as you work; rather than having to open up a render window.
There are comparison commands that compare images in certain directories and provides batch compression.
Download link
