So if your character is always 200 pixels below center or something, you set the yOffset to -200 and it will adjust the shake accordingly.
If anyone is interested I'll post it, but I'd like to take suggestions too.
Description: Shakes screen for a set number of seconds and magnitude. Also has settings for an offset since the shake assumes screen center. You can pick where it shakes. Best case use, attach to your main character who is in the middle of the screen.
Version 0.1: [http://dl.dropboxusercontent.com/u/122492/shake.zip]
Future updates: Option to attach to a sprite location instead of center, so you can pick between offset/stick to sprite. Possibly add orbital shake?