For modelling.Milkshape - Easy to learn, $35. Limited features and uses.Blender - Harder to learn, free. Many more features and uses.For scripting, use any text editor. I use Notepad++For mapping, the built it World Editor, and a program that can export to .dif, such as Torque Constructor.For Decals, faces, and prints, any good image editor that supports transparency.For editting existing music into the proper format, Audacity or Goldwave.For making music, IDK.