I have an native iPhone app written up.
However, I need a couple of graphics yet until I can submit it.
From Apple's App submission page:
"Your application application must contain a flattened, square-image icon that is 57 x 57 pixels. This icon is what will be displayed on the iPod touch or iPhone home screen." (.jpg, .jpeg, or .tiff)
And a "large image" icon:
This will be used to feature your application on the App Storefront. To be featured prominently on the App Store we recommend you provide an attractive, original icon that meets the following requirements:
512 x 512 pixels (flattened, square image)
72 DPI
.jpg, .jpeg, or .tiff format