2018 Update - Please don't use this info !

I'm leaving the below post for reference purposes.

Please read Apple's documentation Human Interface Guidelines - Launch Screens for details on launch screens and recommendations.

Thanks
Drekka

July 2012 - As this reply is rather old, but stills seems popular. I've written a blog post based on Apple's doco and placed it on my blog. I hope you guys find it useful.

Yes. In iPhone/iPad development the Default.png file is displayed by the device automatically so you don't have to program it which is really useful. I don't have it with me, but you need different PNGs for the iPad with specific names. I googled iPad default png and got this info from the phunkwerks site:

iPad Launch Image Orientations

To deal with various orientation options, a new naming convention has been created for iPad launch images. The screen size of the iPad is 768×1024, notice in the dimensions that follow the height takes into account a 20 pixel status bar.

Filename Dimensions

• Default-Portrait.png * — 768w x 1024h
• Default-PortraitUpsideDown.png — 768w x 1024h
• Default-Landscape.png ** — 1024w x 748h
• Default-LandscapeLeft.png — 1024w x 748h
• Default-LandscapeRight.png — 1024w x 748h
• iPad-Retina–Portrait.png — 1536w x 2048h
• iPad-Retina–Landscape.png — 2048w x 1496h
• Default.png — Not recommended

*—If you have not specified a Default-PortraitUpsideDown.png file, this file will take precedence.

**—If you have not specified a Default-LandscapeLeft.png or Default-LandscapeRight.png image file, this file will take precedence.

This link to "Apple's Developer Library" is useful, too.

As of July 2013 (iOS 6), this is what we always use:

IPHONE SPLASH Default.png - 320 x 480Default@2x.png - 640 x 960 Default-568h@2x.png - 640 x 1096 (with status bar)Default-568h@2x.png - 640 x 1136 (without status bar)IPAD SPLASH iPadImage-Appname-Portrait.png * 768w x 1004h (with status bar)iPadImage-Appname-Portrait@2x.png * 1536w x 2008h (with status bar)iPadImage-Appname-Landscape.png ** 1024w x 748h (with status bar)iPadImage-Appname-Landscape@2x.png ** 2048w x 1496h (with status bar)iPadImage-Appname-Portrait.png * 768w x 1024h (without status bar)iPadImage-Appname-Portrait@2x.png * 1536w x 2048h (without status bar)iPadImage-Appname-Landscape.png ** 1024w x 768h (without status bar)iPadImage-Appname-Landscape@2x.png ** 2048w x 1536h (without status bar)ICONAppname-29.pngAppname-29@2x.pngAppname-50.pngAppname-50@2x.pngAppname-57.pngAppname-57@2x.pngAppname-72.pngAppname-72@2x.pngiTunesArtwork (512px x 512px)iTunesArtwork@2x (1024px x 1024px)

For iOS7 create launch images in the following sizes:

For iPhone 5 and iPod touch (5th generation):

• 640 x 1136 pixels

For other iPhone and iPod touch devices:

• 640 x 960 pixels
• 320 x 480 pixels (standard resolution)

For iPad portrait:

• 1536 x 2048 pixels
• 768 x 1024 pixels (standard resolution)

For iPad landscape:

• 2048 x 1536 pixels
• 1024 x 768 pixels (standard resolution)

See iOS 7 Design Resources > iOS Human Interface Guidelines > Launch Images

UPDATE 1

For iPhone 6:

• 750 x 1334 (@2x) for portrait
• 1334 x 750 (@2x) for landscape

For iPhone 6 Plus:

• 1242 x 2208 (@3x) for portrait
• 2208 x 1242 (@3x) for landscape

UPDATE 2

For iPhone X:

• 1125 x 2436 (@3x) for portrait
• 2436 x 1125 (@3x) for landscape