Winterboard - Give your iPhone or iPod Touch a graphical overhaul!
Springtomize - Tear down the walls
Dreamboard - DreamBoard lets you take control over the homescreen of your jailbroken iPhone.
Five Icon Dock - Tweaks the dock of your jailbroken iPhone so that it can fit five icons instead of four.
Lockinfo - You can find this app in Cydia - Tweaks.
Five Icon Switcher - This puts more icons into the iOS4 multitasking bar, instead of the usual four.