If you're jailbroken on iOS 5 you'll definitely want to check out the newly released Springtomize 2. It's by far one of the easiest ways to customize your device running on iOS 5. To start customizing just purchase Springtomize 2 in Cydia then pop into your Settings app and start tweaking every little aspect of your springboard easily and directly from your device.
Theming your iPhone is definitely one of the perks of being jailbroken. Sometimes a really nice theme comes along that completely changes not only the design but the way you use your iPhone. This may be the case with the OS X Ultimatum theme by Modmyi forum member SirTimothy1.