One nice feature about having an iPad in the classroom is that you no longer need to worry about the document camera – one less piece of equipment to fiddle with. There are a few apps that will replicate the document camera on your iPad. The nice part of using your iPad is that you are free to move about the room with it. You can bring it to your students rather than have them come up to the board. Also if there is a problem you want to use in multiple classes, you can just take a photo of it and then erase annotations each period. You can use the iPad camera to take photos of student work. Once you are comfortable with the iPad, there is little reason to keep that document camera around.
I would recommend 2 apps. Stage is a basic one from Belkin that will allow you to annotate and bring in labels. The newest version does charge for recordings and adding shapes which can be annoying to get a pop-up when selecting a premium feature. My preferred app is Doceri which is free and has many tools included in it. There are several backgrounds such as graph paper, maps, etc that you can use in addition to anything in your photo library. Doceri will also create a PDF of your steps that you annotate if you like. There is a small watermark on the Doceri PDF that can be removed for a small in-app purchase ~$2.99. Here is a short video that I did showing you how you can use Doceri.
If you like using a stand, you might want to consider this one – Justand V2 – $99: