Photoshop is great for creating images. I'm sitll using Photoshop 7 but it works. Also, if you are like me and don't know how to write animation into GIFs, image ready makes it VERY easy. You can access it from photoshop and it will make animations out of the frames you create.
I have photoshop cs4 extended, i think it is best for sigs and/or any other graphics! But if you want to use it you will need to learn, it is sometimes little complicated:D