Zip case that will fit around Otterbox Commuter?

I can't say for certain, but the Belkin Pleated Sleeve may work for you. I use it in conjunction with the Incipio Silicrylic and it fits snugly but comfortably.

I would suggest using a netbook carrying case for that. I use one for my iPad now and I could certainly see it fitting with the Otterbox case. The one I have now is a Case Logic netbook bag I got at Walmart for 20.00. It can fit two ipads back to back on the main compartment and I can keep my phone and iPad charger as well as headphones and stylus in an outer pocket.

This is the bag I have - http://www.walmart.com/ip/Case-Logic-Netbook-Attache-Case/14650184

My ipad in a commuter case fits in the incase neoprene sleeve. It's a little bit of a tight squeeze but nothing that I think is excessive.

http://www.goincase.com/products/detail/neoprene-sleeve-plus-cl57474