In case you can't wait for iAds to show up on the iPad and there's no way you're going to charge for your free app, Google has just launched new ad formats specifically targeted to iPad apps developers. (based in US and Canada)
Google explains in a blog post:
"The new iOS SDK supports ad serving in iPad apps using three of the most common online ad formats, instantly making it easier for developers to grow their businesses and for advertisers to expand their presence to the iPad.
Advertisers whose campaigns run on the Google Display Network and include text or image ads in the above sizes can now show ads within iPad applications – provided their campaigns are targeting mobile devices or specifically the iPad."
Here's my suggestion, though. If you really care about the look of your application, look elsewhere. Wait for iAds. Make it paid. Think about it.