Banner ads are fine, but if you really want to make a mobile impact, Rich Media is the preferred choice.
A Rich Media ad contains images and videos that normally require some type of interaction and dynamic motion with the user. Ads can expand, float, or peel away from the content of the page. Ads may change when the customer’s cursor passes over it. Streaming video or a stock ticker are examples of basic types of rich media.
Of course, rich media will cost more than a simple banner advertisement, but you’ll see a significantly higher click through rate — usually about 4x greater. The greater click through rate, coupled with an improved recall rate, should give you enough incentive to consider doing more than just a banner ad with your mobile advertising.