Well depends i guess on what your looking to do. For example if your making games those plug-ins plus the free ones around the forums(which you have no reason not to use
)should be more then enough(I only have dark AI and barely have used it although its been excellent when i have used it). If you want to make a level editor with your game blue Gui i hear is great although you can manage just fine with your own Gui system or even some free Gui's floating around like Aaron millers widows Gui plug in which i have used in my editor(s). Hope this helps