Apple's iAd Producer is a Mac studio for creating iAds
Speaking of templates and components, Apple has thrown in a selection of pre-built animations and effects, as well as Apple-style buttons, sliders, and other interface elements. iAd Producer also comes with an iOS 4 simulator, so you can see (roughly) what your finished ad would look like on various iOS devices. Live testing over your carrier network is also available, but only to existing iAd customers. The app is available for free in the iOS Dev Center, provided you're a paid member of the Apple Developer Program.