My phone is jailbroken. To some, this is a warning sign. To others, it means a whole new realm of possibilities. Because I have rebuilt my phone about four times in the past three months, I figure it's about time to make a list of my favorite apps for the next time I rebuild it.
This is by far the most useful app I have come across. Moving all the toggles in settings such as bluetooth, wifi, airplane mode, etc. into a drop-down menu is just awesome.
Most won't see functionality with this, but restoring files, saving videos and pictures, etc. is much easier with an SFTP client than iTunes.
Making the iPhone look pretty is, to a lesser degree, important. By default, Winterboard allows you to have photos as wallpaper, remove icon labels, and extend the beauty of your iPhone desktop and sounds with misc add-ins and features.