As you might imagine from its name, ClipboardEdit for Notification Center makes it possible to edit the contents of your iPhone clipboard. The clipboard will contain the latest text that was cut or copied on your iOS device. ClipboardEdit actually adds a widget to the Notification Center that displays the text (if any) stored in your clipboard.
From there, you can edit the text in the clipboard or type something new and it will automatically be saved. The next time you use the paste function, your new clipboard text will be pasted. ClipboardEdit requires iOS 5 or later and a jailbroken device.