I have my iPad in a bag now but I really need to either get a skin or a case for my iPad or get a bag with a proper compartment for it so I do not scratch the back. I'm waiting for a case that has the features of the smart cover with the protection of the iPad 1 case.
I don't have a real case for the iPad yet, so when I need to take it to my classes, I use the gray polyurethane Smart Cover and put the iPad in the Apple Sac that I no longer use for my MacBook, and I carry this in my backpack.
I bought a rickshaw messenger bag which I use. Their messenger bag is probably the most comfortable messenger bag I've ever used. It is pretty minimalistic in that it only has 2 compartments, 1 for the ipad and 1 for everything else. It has velcro so that you can add onto it. It also has 2 small pockets, 1 which I use for pens and the other for my cell phone.
It is also a nice size at 10" by 11.25". I hate computer bags that are a lot larger than the devices they are designed to hold.