A new tweak available in Cydia for jailbroken iPhones and iPod touch will provide you with a 3D cube effect for your homescreen ‘springboard’ icon pages (shown in the demo video below).
If you are familiar with Compiz on Linux, this is pretty much the same effect, but also includes a few customization options including the ability to have the cube transition on the inside or outside.
Barrel is a tweak available through the BigBoss repository in the Cydia App Store for $2.99. The UI tweak will not add an icon to your springboard, but you can configure the tweak from within the Settings.app.
Barrel requires iOS 4.0+ and is not compatible with iPad or SBRotator.