For a suite to be useful, it needs to support the applications people use.
But this also has to be carefully balanced -- every application that is skinned adds time and effort to the project. So what do you think would be the list of core apps that need to be skinned for something to be complete for the mainstream user?
Here's what I would pick:

IconPackager for the icons
CursorXP for the cursors.
WindowBlinds for the GUI
DesktopX for the desktop
ObjectBar for the bars and menus
Windows Media Player for the MP3 player (or Winamp)
Maybe Trillian but probably not (I use MSN now).
And WinStyles to put it all together.
What apps do you think really need to be skinned for a complete suite?