Vivek Ramkumar and Paulo de Renzio (an ex-ODI fellow) have a new paper on the role of donors in encouraging budget transparency.
One point they make is the distinction between the capacity of the government to produce data, and its willingness to make it publicly available. In Southern Sudan the hard work is done, there is actually a pretty sophisticated budget system by African standards (activity-budgeting!), and reams of data. All that is needed is a nudge to encourage this information to be made publicly available. Perhaps donors could fund a Ministry of Finance and Economic Planning website, allowing information to be made easily available to journalists and the public.