Technically BiteSMS is not a tweak it's an app. That being said it is the first and foremost BiteSMS is the first App that gets loaded on my jailbroken devices. I don't know if I can go back to stock iOS because of this one app alone. This is worth the $8 all day long because it allows you to respond to SMS within any app, no more switching between apps to answer a text. Also it lets you customize the colors, blacklist people so that their texts don't notify you and it allows you to make as many quick compose messages that you can easily send to people as a reply. For instance if I press one of the volume buttons I can then tap the screen and it gives me a popup to text until my heart is content.
Written by Ellyn Gray. You can find Ellyn on Twitter