Do remember, though, that there is a fine line between intriguing and annoying. If the look of an ad is too busy and jarring, many people will scroll or click immediately just to get away from it. Bold but simple, that's the ticket. The number-one feature most commonly associated with banner ads is animation. Yes, the animated GIF is by far the most common format for Web banners.
Animation is the realm in which it's easiest to go overboard.
Even though you think that army of morphing elephants makes an unforgettable statement about the product, it may not have the desired effect on your audience. A little subtle animation goes a long way. Fortunately, we're limited in our animated exuberance by file size. Most sites that will host your banner have strict limits, which can be too easily exceeded. So practice moderation.