These packs contain DDS files for command card unit/building icons, hero icons (the small ones that show up just above the command card), wireframes and shield wireframes. They are divided in WoL packs, HotS packs and Fan-made packs (this last one still to be released).
Older numbered packs include a wide variety of things, these will be removed as soon as I include all the new 3 packs.
Check the pack's description for the complete list of files.