What is your recommendation for a large backpack for traveling?

Currently I have the Medium Tenba rolling backpack: http://www.tenba.com/Products/Shooto...ium-Black.aspx
The problem is that it is not comfortable to have it on your back. It is more a rolling back. I would have something which I can carry on my back for an hour without killing me. I shoot a lot of destination weddings and the way I carry my gear is very important.

I want a backpack, which is:

- large
- fits into most airplanes bag compartment
- waterproof, and
- durable.

It doesn't have to have wheels.

Can you recommend me anything?