When creating a new universal IOS app you need to create a minimum of 6 launch images to support the iPhone and iPad (both including their retina displays).

For the iPhone you have it easy, only 2 are required.

Default.png – 320 x 480
Default@2x.png – 640 x 960 

For the iPad there are a few more:

Default-Portrait.png – 768 x 1004
Default-Portrait@2x.png – 1536 x 2008
Default-Landscape.png – 1024 x 748
Default-Landscape@2x.png – 2048 x 1496

You can specify images for Landscape Right and Left and also Portrait Upside Down using the names below:

Default-LandscapeLeft.png
Default-LandscapeRight.png
Default-PortraitUpsideDown.png

For more information on Custom images and icons visit the apple developer site