Part of the recent December release for Windows Azure included an overhaul of the billing portal. You now see a visual representation of your resource allocation (for trials and MSDN), and how much you have used for the month towards that allocation.
In this screen shot, I am showing some of the bars for compute, storage, and database.
The portal also lets you now download your billing data as a CSV file. This is important for those customers that need to break up their charges, and do some pass through billing. Or maybe they want to run a cost model to predict costs with usage curves.
You can also change how you are billed, and even cancel your subscription.
I have created a short video to show you how the billing portal works.