I'm sorry if this isn't the right place, but I had a cool Idea for a tool, but it will probably take a lot of scripting.
I enjoy 3d modeling, and I really enjoy editing textures, and one of the easiest ways to make a new texture for a model is by making a collage of many source images. In most 3d modeling programs there is a universal manipulator tool that allows you to move, scale, and rotate the model, face, or vertices you are working on at the time. I realize that there is already a rotation tool, a scale tool, and a movement tool in the gimp, and that in the scale tool you can already move the scaled layer.
I would like to see a tool that allows the user to make general manipulations of layers like the universal tool does in a 3d modeling suite. One tool to move, scale, and rotate layers easily and quickly, possibly adding the skew and perspective tools to the widget as well. I realize that this would not be a simple plugin or filter, but a brand new tool, and would likely take a lot of effort to implement, I just wanted to put that idea out there. A streamlined multi-tool that can do all of the basic physical manipulations of a layer by itself.