Winterboard - Give your iPhone or iPod Touch a graphical overhaul!
Lockinfo - You can find this app in Cydia - Tweaks.
Cydia - An alternative app store for jailbroken devices.
Springtomize - Tear down the walls
App Switcher Rotator - This plugin rotates the icons on the iOS4 multitasking bar to the current app's orientation.
Dreamboard - DreamBoard lets you take control over the homescreen of your jailbroken iPhone.