Preview pdf markup on iPad?

I've always loved the functionality Preview.app provides for marking up PDFs. Using Dropbox allows me to easily see these changes across my mac's, but I'm stumped as to how to not only see, but continue to markup PDFs when I'm using my iPad.

Is there a native app or setting I'm missing? I've tried using iBooks, but I cannot annotate there on a pdf like I can an ePub. If there isn't a way to do this out of the box, does anyone have a favorite third party solution?