After seeing Bond1's thread, I also forgot I use a program that I have not seen mentioned here. If your are after a quick .dds and .tga image viewer, try Image converter plus. I dont own a full edition, and only ever tried the demo, and is still active on my computer (like no trial) however is very limited. The reason I have this program installed, is if you right click on your image so the file properties show, the program adds a small image viewing window. So you can view the image without having to open it. Can save some time when looking finding textures.
http://www.imageconverterplus.com/
Working on a new title, planning in progress.