Sizes: 29x29, 48x48, 57x57, 72x72
For all the above: PNG, No Transparency, No Layers, 72 PPI
512x512, TIFF or JPEG, No Transparency, No Layers, 72 PPI
From Apple's site:
An iPad application needs a 72 x 72 pixel application icon...
You also need to supply an approximately 48 x 48 pixel version of this icon for display in Spotlight search results and in the Settings application (if you provide settings).
As with iPhone application icons, iPhone OS 3.2 automatically adds the following visual effects to your iPad application icon:
* Rounded corners
* Drop shadow
* Reflective shine
To ensure that your icon can take advantage of these visual enhancements, produce a 72 x 72 pixel image in PNG format that:
* Has 90-degree corners
* Does not have any shine or gloss
* Does not use alpha transparency
Important: Be sure to create an image that completely fills the 72 x 72 pixel area. If your image boundaries are smaller, or you use transparency to create “see-through” areas within it, your icon will appear to float on a black background with rounded corners. Icons like this are strongly discouraged on iPhone, but they are especially undesirable on iPad because people can display custom pictures on their Home screens. An icon with a visible black background looks very unattractive on an iPad Home screen.