ipad:
Default-Portrait.png * 768w x 1004h

Default-PortraitUpsideDown.png 768w x 1004h

Default-Landscape.png ** 1024w x 748h

Default-LandscapeLeft.png 1024w x 748h

Default-LandscapeRight.png 1024w x 748h

Default.png Not recommended

iphone:
Default.png 20×480 or 320×460
Default@2x.png iPhone4 640×960 or 640×920