Many websites offer free banner creation online, such as My Banner Maker and 123 Banner, Where you can upload your own images or use some of the preset backgrounds, then there are several options for text and animated (flash) banners. However i prefer to use Banner Sketch because of its saving feature which lets you type in your email address to see all the banners you have created, it also has a save code scheme which allows you to save the settings of a banner that you haven't finished yet and come back to it within the next five days.