Fire in the Sky
Great sunsets are one of my favorite subjects. The longer the focal length of the lens you are using, the less area of colorful sky you need to have for a great picture. In other words, a long focal length can capture a great picture of small sunset display. The sunset in this picture was incredible regardless of the focal length I used.
Here is a tip for you: If one of your borders is a solid color (preferably black or white), you can easily add to it later in post processing. Here, I framed the picture so that I had just enough black on the bottom of the frame to allow more black base to be added later in Photoshop. Thus, I get a higher resolution final image with very little work.
Camera and Lens Settings
300mm f/5.6 1/100s ISO 160 5616 x 3964px