The Axio tank bag fits pretty well. I have one.
What you see is the collapsed position. It expands another 1.5-2 inches vertically if you unzip it.
I like this because it's rigid and you can rest your chest on it (very comfy riding position, actually).
It also has a safety strap, which clips around the handlebar. That's useful when you refuel, because you just lift the bag up and flip it forward/to the left, and let the strap support it. In other words, you don't need to find a place to put the bag when you're at the gas pump.
The map pocket on top doesn't look like it'll last all that long (it's vinyl), but no biggie. It's a separate piece, so if it does buy the farm I can just use the bag without it.