SBRotator by Elias Limneos ($1.99)

If you're like me, you wonder why Apple doesn't have a widescreen Springboard (aka desktop). Thanks to Elias Limneos, you now can! This tweak even works in various other parts of the iPhone OS such as Settings Menu, Youtube, and more!

Note: I suggest you have SBSettings installed before installing SBRotator for easy on/off operation.

This application has no Springboard icon, but does have settings you can change in the iPhones main settings menu.

Once installed, re-spring and turn your phone 90 degrees (left or right) and your Springboard will go into widescreen mode. How cool!

I only changed these settings to make the app look better:
"iPad-style Layout" 4x4 to 3x6 (16 icons max)
"Icon Scale" 85%

Cydia Store Link (iDevice only):
SBRotator 4.x (iOS 4.0+)
SBRotator 4.x SBSettings Toggle (iOS 4.0+)

SBRotator 3.x (iOS 3.x)
SBRotator 3.x SBSettings Toggle (iOS 3.x)